A: Well, if you’re going to have a serious relationship with the guy, or at least any kind of future, his family is something you might want to know, right? Ignoring it forever isn’t a viable option, no matter how worried you are. In-law problems aren’t exactly uncommon but they are pretty nerve-wracking and sucky in a whole bunch of ways. They can make it difficult to get anywhere with them, especially if your boyfriend/girlfriend thinks you don’t mesh well with his family.
And family is so important, yeah?
I think a better way to look at this is the attitude you should go into the dinner with. Don’t go into meeting his family with the already set assumption that his mother and sister are going to be hard on you. Don’t go in assuming they won’t like you, for that matter. After all, they, like you, don’t know what they’re coming up against, either. They don’t know you. All they’ve been told is what they’ve heard, too. And who knows, maybe all they’ve heard is your praises, especially if they’ve been chatting with their son/brother.
It’s a pretty good indication they want to meet you if they’re agreeing to a dinner with you. That’s a good sign they’re already open to whoever you are and the fact that their son/brother is dating you. You should be open, too.
Don’t be nervous, it’s just another step in your relationship. Take it in stride and maybe…stick close to the boyfriend during the dinner if you’re worried. If anything, it couldn’t hurt.