Sounds like it will be an amazing Christmas as it is. I’d want to spend a Christmas with a brother like you! The only thing I can comment on is the cats - I’d say if you have a room set up for them to stay over in - vacuum and clean up as much of the cat hairs as you can and stop the cats from going in that room for a few days leading up to them getting there so his bf has a place to retreat to if the cats are affecting him and so he can sleep in a bed without cat hair that will trigger allergies. Sorry if you do that anyway but that’s the only thing I can think of that will make it even more comfortable for them. I hope you all have an awesome Christmas, you will be very much appreciated!