You realize that it's okay to break off an engagement, right? You don't have to explain yourself to anyone, and they aren't the ones who are going to be living with the man (and his Drisella of a daughter to your son's Cinderella...Cindero?) every day. If they have an issue, then *they* can marry him.
Before I married XH, we broke off our engagement for about a week, then postponed our wedding. I was mortified, but still screwed up in the head enough to think that I wanted to work it out. The abuse wasn't apparent then, but he was starting to show some control issues. Now, I wish I'd just left the damned engagement broken. I really wished I had run when I had an unsettling feeling of dread just before the wedding. I couldn't place it, and just thought it was nerves.
Ending any major relationship in which others are invested, whether an engagement or a marriage, is difficult. It takes courage, and as doglove said, it earns you respect. I will reiterate that it is a hell of a lot easer to end an engagement than a marriage, and I guarantee you that nobody will think less of you for it. And those who do have their own issues that you don't need to deal with.