Very sorry to read this.
Families and weddings are a nightmare but such a shame that yours have made you feel so upset about your wedding.
As for running away to do it there are so many places you can go to do it.
Gretna Green if you don't want to go far.
Or you could get married and combine it with your honeymoon.
Cyprus, Italy, Maldives, Mauritius, Florida, in fact anywhere.
Or if you want something a little more wacky you could do Vegas.
And then if you wish you could have a party when you return. You could even do it so that no one knows you are off getting married and just think you are having a party, until they get there.