That was part of what broke up my first marriage. The in laws wouldn't mind their own business. I would definitely think things through before deciding to marry this guy, especially if he tells his mother everything and talks about you behind your back. Your children should be accepted, also. After all, kids don't have a choice with what happens when parents aren't together. If it were me, I would probably turn and run the other way, also. There shouldn't have to be "sides" in relationships, especially when dealing with your fiance's mother. Just my 2 cents
inthedark