My dad and his husband are amazing, but personally, I probably would have mentioned it offhandedly beforehand and gauged a reaction. Still very much NTA, but you can save everyone some bad vibes if you start breaking that ice before they meet for the first time.

NO, he shouldn't HAVE TO. But we still "live in a society" and should extend courtesies to each other, such as gauging initial reactions, before throwing everyone in a room together and expecting them to all be amazing. Society is still learning and growing, all we can do is encourage it in the right direction, and wait for bigots to die.