For the most part, the core gang of friends in The Big Bang Theory are each others family - but from time to time, their actual relatives pop in as well! Some only show up for an episode or two, and some are only mentioned (including many siblings who don't even get named). Others, like Leonard and Sheldon's mothers, become fairly big characters of their own, and show up on a regular basis.
But between all the siblings, cousins, and parents mentioned on the series, which are the ones that fans would most like to be related to themselves, which are the most enjoyable to watch, and which make us feel sorry for the people that they are related to?
Best: Priya (Raj's Sister)
Priya shows up in the fourth season of the show, where it's revealed that she has previously had a fling with Leonard. When she comes back to California temporarily, this spark is rekindled, and the two end up in a relationship over the course of two seasons. While she frustrates Raj from time to time (especially with her relationship with his friend), it's clear that these two are actually very close. They have their disagreements, but they are great siblings to one another, and clearly friends as well as brother and sister.
Worst: Alfred (Leonard's Father)
Leonard's father doesn't show up very often in the show itself, but Leonard tells a few stories about him over the course of the show that definitely reveal the kind of man that he is. Leonard definitely didn't have a great relationship with either of his parents growing up, and while a lot of the blame for this falls on his mother, his father has to take some responsibility, too. Leonard makes it clear that his father was distant and rarely around, and didn't show him much affection.
Best: Missy (Sheldon's Sister)
It would have been nice to see more of Missy on the show, but she only appeared in a couple of episodes (and multiple mentions, as well as one off-camera scream). However, what fans do see of her, she's a great character - and not a bad sister, especially given that her brother is Sheldon!
Missy truly cares about him, and makes that clear, and she is kind to his friends and welcoming to Amy when Sheldon marries her. She is also able to make Sheldon listen to her, which is a truly impressive ability!
Worst: Michael (Leonard's Brother)
Leonard's siblings, Michael and an unnamed sister, aren't bad people, but fans definitely feel for Leonard, as it's clear that he feels constantly negatively compared to them. It's heartbreaking to see a man who is so successful feel that he will never be good enough, and while neither sibling appears on the show, that in itself is a little eyebrow-raising. Where were these siblings at his wedding? Why did they never come visit? Why aren't they there for Leonard, given that they all had the same loveless upbringing?
Best: Mrs. Rostenkowski (Bernadette's Mother)
Bernadette's mother doesn't show up often on the series, and she's a bit of a complicated one - but based on who she is during the events of the show itself, and not during Bernadette's childhood, she's definitely more on the lovable side. She definitely wasn't always the most supportive of her daughter growing up (Bernadette mentions that she was used to dealing with kids at the illegal daycare that her mother ran), and she was clearly overbearing (she would lay out Bernadette's clothes and check on her eating habits as an adult). But she is absolutely motivated by love and care for her daughter, and she supports her relationship and shows up at her wedding, and is just as welcoming and motherly toward Howard, too.
Worst: Sam (Howard's Father)
Howard's dad doesn't show up at all, but he's a huge presence in the show because of how much he hurt Howard as a child. Sam left Howard and his mother when Howard was 11, and in a lot of ways, Howard never got over this feeling of being abandoned.
A lot of his saddest stories tie back to this traumatizing event, and it's heartbreaking to think of a young Howard struggling with the idea that his father didn't want him. Given that fans learn essentially nothing else about him, it's easy to hate Sam.
Best: Wyatt (Penny's Father)
Penny's family isn't a huge part of the series, and of all her relatives, her father gets the most screentime - and deserves it, as he quickly becomes a fan favorite. While it definitely seems like he was a far from perfect father growing up (as he wished Penny was a boy, and treated her like one until she hit puberty, when he became distant), as an adult, he has a solid relationship with his daughter. He is caring, and also knows how to help her make better decisions without pushing her too hard. He's always been supportive of Leonard and their relationship, and in many ways, became a father-figure for Leonard, too.
Worst: Mike (Bernadette's Father)
Mike has his good points, of course, but overall, he's not a well-liked character or a particularly great parent. He's incredibly overprotective with Bernadette, and is very intimidating when meeting Howard. In fact, Bernadette's father and her husband never really manage to build a great relationship, and this is largely down to Mike, who makes no secret of the fact that he thinks Howard isn't good enough for her. There are also hints that Mike has some concerning prejudices and views, especially when Bernadette lists things not to mention to him, which include "Jimmy Carter, gardeners, foreigners, homosexuals, Sean Penn, Vatican II, organic food, designated hitter rule, gun control, recycling," and the fact that Howard is Jewish.
Best: Mary (Sheldon's Mother)
Everyone, from the fans to the rest of the characters, adores Sheldon's mother, and it's easy to see why. She and Sheldon may not have the easiest relationship, but she's a loving mother who is willing to do whatever she can to support her son. She doesn't always understand him, but she does also accept that he doesn't live the way she wants, and Mary knows when to draw a hard line and when to be flexible.
Worst: Beverly (Leonard's Mother)
Beverley is probably the most loved of the main characters' parents, and she's an incredible character on the show. Her arcs with Sheldon and Penny are amazing, and her growth in her relationship with Leonard is heartwarming to see. However, when it comes to judging how she is as a parent, well... she's pretty terrible. When Leonard was a child, his mother was cold, unloving, and incredibly strict, and treated him as an experiment. She compares him to his siblings and rarely shows him any affection - but she does grow by the end of the show, and when she thanks Leonard for his forgiveness, it broke fans' hearts in the best possible way.