I'm not sure where to start
I would suggest some private lessons and then try to communicate a little with your relatives that speak Polish.
Nothing can beat total immersion.
This is probably true although very difficult I imagine. I imagine that most people who do the total immersion thing also get lessons and really give the lessons 100% because they are not going to manage successfully otherwise, they have to learn the language, that as soon as they step outside the door they are confronted with what they have learnt is a huge advantage.