You're a good daughter OP and I totally get it. I love my dad and feel very protective of him as well. I probably wouldn't have called the friend but understand the concern. Wish him well!

OP, honestly I think it may be more to do with his "friend" than your Dad. Perhaps this couple have just been polite thus far but really don't want to keep up with it. They tried to come up with a kind excuse instead of saying, "Hey John, we really can't stand Sue so can you stop bringing her around?"