How do I come out?

I need some help on how to come out. I am bisexual and asexual, but my parents are always talking about how “Oh, I can’t wait for grandchildren!” and “The man you’ll marry will be very lucky.” They aren’t homophobic, but they assume that I want children and that I’m straight. It’s hard because they bring it up in every conversation and I have to suppress myself from shouting at them for making me uncomfortable, or else I get punished. If I could have some help on what to do, that would be amazing.

I’ve definitely tried to be funny but they just don’t seem to get it. They always take it lightly and they think I’m not being serious.