I am scared of my fiance's family--so much so that I'm worried about having his baby?

I'm pregnant but scared of the fact that I don't like my fiance's family. They are "enablers" and they are all controlled by the Grandma. She has a strong personality like me and I don't think I'll be able to control my thoughts around her. She has raised children and grandchildren who are wholly dependent on her and not to be mean, but they're a little "weird." He has an uncle who is convicted molester, a niece who refuses to wear underwear (she's 7) and can't read or write. That's just the tip of the iceberg. On the surface they are all nice but how do I say this...kind of undereducated and a little ignorant. And that's OPPOSITE of my family. Should I be concerned? Also worried about our parenting styles being different...he doesn't say no to the kids and I do--and I think this will be a problem with discipline."kids should do what they want to do and not be forced to do anything" is what the matriarch of his family says and I can't imagine having every Xmas with them! Stressing out