Poor OP. ?
I think They are seeing how far they can push you. Don't let them get away with it PLEASE! I would be horrified if my children spoke to their gran like that. If you don't want to tell your daughter then try to deal with it yourself.
If they call you a witch again say you'll put a spell on them! Maybe jokingly call your daughter at the time & say "Ha ha, your sons think I'm a witch. Which animal shall I turn them into?" Don't go all the way out there for them to torment you
Army horses loose on London streets