Are pack dynamics inherently sexual?

Every omega and alpha in the pack has needs that have to be sated, right? So, my question is, are all the members of a pack involved sexually or is there a designated breeder, for the lack of a better term? I wanna write stuff about packs, but I'm still very confused about how it works. It's especially important for me to know because the story I'm working on includes a pair of siblings who join the same pack. How am I supposed to deal with that? I want to know what truly entails to be in a pack, both as a family of sorts and the sexual aspect of it... Sorry if it's a dumb question, I know there's no set rules, but some guidance would greatly help.