Yessss this turned into a rec list but here we go
Marvel Exiles vol 1 (2001-2008). Great crash course in the Marvel Multiverse, Highly recommended for MCU fans just getting into the comics. I haven't read much of the more recent series but I hear good things about what they did with my girl Nocturne (whose further adventures were chronicled in House of M and Excalibur)
(event) Marvel's House of M. Following Wanda Maximoff's nervous breakdown after realizing her sons had always been products of her chaos magic, and influenced by her twin Pietro's whisperings about how they should live in a better world, Wanda creates a false reality in which her family are the ruling body and mutants, not humans, are the ruling class. Breaks into pieces after she realizes it's not real, after which she whispers the famous words 'no more mutants'. Immediately followed by Decimation, then events lead into the Civil War.
Marvel's Young Avengers (2004-2016). Takes place immediately following the House of M/Decimation event. Great from start to finish, written by Allan Heinberg, famous for The OC and creator of Grey's Anatomy (hence there being a Teddy Altman in both). Everybody's queer, everybody's sad. Also the tie-in with Civil War and the follow-up The Children's Crusade is outstanding. YA vol 2 is okay but I wish people had actually bought it so the story could have played out the way it was supposed to. (also Emperor Hulkling & Wiccan because my boys grow up and get married and i'm still not okay)
Marvel's What If? vol 114: Secret Wars 25 Years Later (1998). Tie-in to the Secret Wars event from 1984. The heroes and villains who survived the battle have settled down and raised families, and their kids, as kids do, want something more than the provincial world they grew up on.
Anything that has to do with DC's Flash Family before the New 52 rewrote their canon.