They'd probably disagree on what they consider important. But that's mostly because Istredd is a busybody and likes to know things. He did tell Lucifer he informed Castiel of their friendship (still a friendship at the time) and left it fairly ambiguous as to what happened. He suspects Lucifer wouldn't be impressed by Castiel's promise to keep Istred safe ... and might even be very irritated by it.

You three make me glad I never had siblings. Or at least I don't think I do. It wouldn't matter if he did. Most of them would be older by now or already dead. Not a whole lot of people in their 80s and 90s comfortably living in the continent. Istredd has no family but the one he is quietly making day by day in the castle.

He knows befriending all three of them was asking for trouble, but he has been clear where his loyalties lie at the end of the day. In bed with this troublesome creature.

I'm sure it does, but it's not going to be easy to go back there. Alas. His great regret. Although he has some sentimental feeling toward the place too. Their first trip as a couple. Don't perceive him. Anastasia might like you considering Ambrose does not. Saying out loud what seems obvious. Now their sibling relationship does remind me of you all.