I've gotten along really well with her family, they feel more like home than my own family. But we've only been together a few months so it makes sense haha. I didn't mention it to anyone except in this topic and to my absolute closest friends, her mom just found out by reading her signs when she said she was really fatigued; she asked about other things and said "Sounds like you're pregnant".
Well that's good, will definitely make it easier... it would suck if you didn't get along with her family. Hopefully this brings you and your girlfriend even closer together, I imagine it'll be tough having a child with someone you've only been with for a few months, but you can do it if you really want to, which it sounds like you do. And ah, I suppose moms can always tell.