Anonymous wrote:

"I truly love your daughter, and I wish the best for both Sally and John. I know this is a very difficult time, but I think it's best we stay out of it, so that they can make a mature decision on their own. Any interference by others may come back to haunt their relationship in the future."

Yes, some variation of this, perhaps shorter and without the "we".

I am so sad for Sally and John but I respect that they are adults and will work out their relationship however is best for them. I wish them both the best."

And I would leave it there. If they persist I'd say "I'm sorry but Sally and John are adults. I'm not going to get involved."