Love / South American living in the US, meeting her Polish parents!! [3]

Hi guys
I'm a South American living in the US.
I met my girlfriend in America, she went to Poland for 20 days to visit her family.
Im going there in two weeks and we are going to fly back together.

I want to meet her parents and they want to meet me, they kindly invited me to their home, I will be there for 4 days before coming back.

I'd like to know some recommendations because this is a girl a want for my life and I'd like to communicate that to her parents in some way. I dont speak polish and they dont speak english. I would like to know if there are some customs or way to be with them, from shaking hands, to hug or kisses on their check, wherever polish parents would expect from their daughter's boyfriend.

Some background info, my girlfriend and I live together, the parents have known for the last month, but of course they dont like the idea, but she and I have talk about our future and marriage already, eventhought we have no formal date yet (she talked to her parents already about it), at some point I would like to talk to them about it and ask their blessing, etc, but not yet, that will be for my second trip.

We love each other and share a lot on our lives, and the way I feel and she feels we are giving our steps to build our lives together.

Any advise will be useful.
Thanks!!!