Meeting my Czech mother-in-law (help) (Prague)

Hi there!!

I am excited to go to Czech, tomorrow I am flying there and I am going to meet my boyfriend's parents.

I would like them to have a good impression over me. Buuuut...
Problem n.1 - I don't speak Czech and they don't speak English
Problem n.2 - I am vegetarian and I am not sure how ok would be if I skip some main course during the meals
Problem n.3 - I am going to stay in their place and I don't know if it is polite to offer some help, or I should behave like a regular guest.

I am looking forward to hear hints how to make them fall in love (or like even a little bit) me :D
Thank you very much!
Fernanda