We and our families have been back and forth about this for a decade now and I have seen hundreds of women discuss this topic. There really is only one answer that seems to work. Lie.
I hate lying, but in the first place, it isn't any of their business. In the second place, they are never going to come around. Almost no one does. That's why almost no one births unassisted. You can't change their minds, you can only make everyone stressed about it, including yourselves. Third, you have to do what is best for you and your baby. When it comes down to it, I would tell a million lies if I did it to protect my child.
We no longer tell anyone we are having a UC. If anyone asks, I flat-out lie. I tell them we are going to the hospital or the birth center or that we will have a midwife deliver.
The best option is to never mention it in the first place. If you don't mention it, everyone just assumes that you are going to a hospital, no question, and everything is hunky-dory. They won't even consider asking because nobody considers someone else having a UC. But since you're in our position and already said something, the only thing you can do about it is lie. Nobody is going to be impressed at us having a UC, they just get very concerned and this will have negative effect on your birth and your feelings toward your family.
So sorry you are going through this. :(