My Danish friend attended a Polish course in København. They used a Swedish book, which wasn't the best book I've ever seen, but better than nothing. After a half year he couldn't speak much, but with my help he becomes better and better.
In my humble opinion it's impossible to learn Polish on your own - it's 1. a Slavic language, so different from f.ex. Danish, 2. probably the hardest of the Slavic languages. If you feel determined I can teach you via e-mail, provide grammar lessons and such. There is a language course in this forum - have a try. My choice would be to come to Poland one year before you meet your family and learn the language here.
If you have any more questions or there's anything you'd like me to do - I'm to your service.