None are grammatical. "What will mom and dad say about that?"
My sister has been seeing a lot of men that are way older than her. I ask her:
What's mom and dad gotta/hafta/gonna say about that?
Are all okay?
But I think I've heard them used in conversation or movies.
"What will they have to say about that?" is fine, just not with "hafta" which is not a word. We discourage the use of sub-standard English such as "gonna/wanna/dunno" etc on this forum.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.