First time it came up, I think I would have said, "OK, it's on day/date, right? And I am for sure invited? It's not just immediate family or blondes only or something? Fine. Where and when and what can I bring?" I would have persisted until I got the specifics. At this point, I'd just call Aunt and ask her. I think, as long as you won't take offense if you are not invited, because only dachshund owners may come because of Uncle's new puppy or whatever, it is fine to say, "Cousin Jane acts like Mom and I are coming for sure, but, really, Aunt, are we even invited? Great. So, what day? Time? Your house? Oh, Cousin Fred's, right. Can I bring, or should I call Fred to find out what's needed?" Nothing rude about that among family or close friends -- as long as you are prepared to accept with grace not being invited, just in case.