Both of these dramas focus on a beautiful couple (with the added bonus of the same actress playing the FL) who are facing hardships because of their secret past.
The two couples in these dramas also face the disapproval of their families while also witnessing those around them slowly get married and divorced.
The two dramas also focus on just how far mothers will go to cover their children's crimes. And how parents can sometimes suffocate their children while trying to help them.
The ML's of these two dramas also both dreamt of becoming famous through sports but both had to drop the idea because of something that happened in the past.

Both of these dramas focus on a teenage boy who "attempted suicide" by jumping off of a high building. Both boys end up in a coma and their loved refuse to believe that they were suicidal. As the dramas unfold, both boys are discovered to have been forced to jump off.
Beautiful World is about the issues of jealousy, bad parenting, sexual assault, and school violence.
Nobody Knows is about the issues of cults, being too kind, corruption, and serial killings.

Sunny Again Tomorrow is very lighthearted compared to Hide and Seek.
However, they have very similar premises.
Sunny Again Tomorrow is about the famous CEO of a fashion brand searching for her daughter for 20 years. Meanwhile, her daughter has been raised in another family and has opened her own small clothing shop. The niece of the CEO actually saw the daughter get kidnapped on the day that she disappeared, but she was young and scared so she never told anyone. The daughter falls in love with an office worker, invoking the jealousy of the CEO's niece (the niece has a crush on the ML) who eventually finds out the true identity of the daughter and tries to cover the truth.
Hide and Seek is about two women. As young girls, they exchanged their luck (one was unlucky and the other had good luck, and a shaman exchanged their fates). The two girls do not know each other at all. The girl who took all the bad luck grows up normally while the girl who took all of the luck disappears. the lucky girl's mother who is the CEO of a fashion company desperately searches for her and crosses paths with the unlucky girl.

Memories of the Alhambra is about a VR game turning into real life.
Meanwhile, Extraordinary You is about the characters of a comic book becoming self aware and trying to change their fates.
At first, these may not sound similar, but if you look harder you'll find many similarities.
Ignoring the fact that the relationship in Memories of the Alhambra is hate-to-love while Extraordinary You is more of a soul-mates relationship; the way that the main couple interact and try to change the foreseeable future is very similar. And the premise of both are being stuck in a fantastical world.

Lost Romance is about a woman being sucked into a cheesy CEO-love romance book. She finds out that she's supposed to be the side character that bullies the FL of the romance book and is determined to capture the heart of the CEO while being friendly with the real FL. The relationship is hate-to-love.
Memories of the Alhambra is about a VR game glitching and becoming part of real life (it's hard to explain. Let's say that you were shot in game and die, you die in real life too. And, if you take off your VR glasses, the game console doesn't disappear). The relationship is also hate-to-love.
Both of these dramas focus on the death/coma of an important character and both focus on survivor's guilt.

VIP is a drama less than half the length of My Unfamiliar family. However, they share many similarities.
My Unfamiliar Family is a family drama so it focuses on all family members. Some of these family members have/are cheating on their partners/spouses. And, one of the family members is suffering from depression after getting a miscarriage.
VIP is a drama that focuses on a woman who knows that her husband is cheating on her. The whole drama, she is trying to find out who her husband is cheating with. The wife (the main character) also suffered from a miscarriage.
Both of these have the added bonus of having SHIN JAE HA in them. And in both, he plays the important role of accidently uncovering secrets and comforting the main characters in times of need.

Graceful Family is way shorter than Unfamiliar Family. And while Unfamiliar Family is all about suspense and is a slow-burn, Graceful Family is all about angst and a rushed romance. This may also be attributed to the fact that Unfamiliar Family is 100+ eps while Graceful Family is only 16.
The plots of these two is totally different, however, they have one subplot that makes them similar.
!! SPOILERS AHEAD!!
!!DO NOT READ IF YOU DO NOT WANT SPOILERS!!
!!YOU HAVE BEEN WARNED!!
In Unfamiliar Family, the eldest daughter gets a divorce because she finds out that her husband is gay. This discovery destroys bother her and her husband and they struggle with their separation and coming to terms with his true identity.
Graceful Family has the same plotline. The eldest son of the family is a transgender (so he's actually a female who likes males). When the wife finds out, the two divorce.
Bother of these subplots also have the similarity of the wife desperately trying for children but her husband not cooperating.

Both of these dramas focus on the mysterious past of the parents.
My Unfamiliar Family takes a look at a dysfunctional family who are forced to get closer when the father gets in an accident and loses his families. As the children of the family get into relationships or leave/divorce old ones, the parents struggle with their past of betrayal, cheating, and unexpected pregnancy.
Meanwhile, Once Again is of a lighter tone. It goes over the budding relationships between the children of the family (who have all been married once and are all divorced). The father of the family lost his sister a long time ago and believes that she is dead. However, she is actually alive and the drama follows him as he uncovers the truth behind how she disappeared.

Both of these dramas focus on the love life of the children of a large family. In both dramas one of the children is a player, the other has never dated before, and another is going through the hardships of marriage.
Unfamiliar Family and Father is Strange both focus on a secret that the parents of the families have been hiding for years.
Father is Strange is a really cute and fun drama to watch. It goes over the love of siblings as well as the struggle to accept those that you love. It has the added bonus of jokes about homosexuality.
Meanwhile, Unfamiliar family is a little darker. It goes over the hardships of being considerate towards your loved ones. It also shows the hardships of a being a closeted gay.

Never Twice and Unasked Family both have FL's that have lost their husbands and are raising a young child by themselves. The ML's for both of these dramas are office workers.
However, Never twice focuses on way more families than Unasked Family does. And Never Twice holds a darker tone than Unasked Family did.
Unasked family is about a woman uncovering the truth about her husband's death while falling in love with the office worker who received his heart (her husband was an organ donor) .
Never twice is about a woman uncovering the truth behind her husband's death while falling in love with the nephew of the man who killed him.
The two premises sound really similar don't they?

These two dramas are both lighthearted, comedic, and cute family dramas with disturbingly manipulative villains who both marry husbands who they love dearly but end up making unhappy. Both of the villains either fake a pregnancy or get a miscarriage.
The main couple in both of these is equally as sweet and aesthetic (bless whoever casted them) and are both love-to-hate couples.
Unasked family and Sunny Again Tomorrow both have families that are tightly interwoven with different connections. However, Unasked Family only focuses on 2 of these families while Sunny Again Tomorrow focuses on 4.
The main couple in both of these dramas has an adoptee as one of the characters (I won't point out who as it might be a spoiler).

Basically the plot devices of both dramas are really similar. And the main couples are really worth the watch. However, both of these dramas have different premises. Unasked family is about a single mother uncovering the truth behind her husband's death and falling in love with an office worker (who just happens to have received her husband's heart during a heart transplant).
Meanwhile Sunny Again Tomorrow is about a (45-ish your old) mother who lost her child 20 years ago searching for her child; unbeknownst to her, her daughter has grown up to be the CEO of a small clothing business and is in a relationship with an office worker.

This is a family drama with a similar feeling to Bad Love, however it's more comedic and lighthearted.
Sunny Again Tomorrow is about a mother who lost her child 20 years ago, unknowingly being her child's main competitor in the fashion/clothing industry.
The romance in both dramas is also similar as in the parents of both main couples are against the two being together. There is also a villainess arch in both dramas and both of the drama's villainesses in the same way. The villainesses also both marry men who they end up making unhappy and they keep on digging themselves deeper and deeper graves. Both of the villainesses are equal in their level of manipulation and blackmail.
If you liked either of these dramas, watch the other one for sure!