What would I do? I'd call them.
They didn't RSVP. I know if you are up on ettiqutte that will really bother you. But to the majority of family, it doesn't mean much and with family, its probably, "Why bother. She knows we're coming."
When you call ask them if they are coming and how many are comming. DON'T ask them if they know what RSVP means. Unless you want them to feel chastised and then you may just be there without anyone. And it may bother you for them not to answer, but not near as much as it will bother you to fly all that way and no one show up.
100 years ago only the lowest of low class people wouldn't respond to an RSVP. 100 years ago no woman would even think about living with a man she wasn't married to unless she was paid. But manners aren't taught to kids any more because too many people want to be politically correct. Today, very few women have enough pride and respect for themselves to demand a wedding before sex.
Times have changed for the worse. Good luck to you and yours.