the first question,if you say "i can't marry you"when you are a man,it means "wo bu neng he ni jie hun" but if you are a girl, it mean "wo bu neng jia gei ni"
the second qestion, if you are a man,"marry me" means "jia gei wo ba" or "he wo jie hun ba" if you are a girl ,it means "qu wo ba"or "he wo jie hun ba"