First of all he is adorable!

Secondly, I had Sylvia and Harley for 2 years when I introduced Morty and then a month later Jimmy. 3 males 1 female. Different breeds, but same concept. Here's how it's working out for us. Morty has been with us since June. He has no problems with Syl or Harley. Harley is very protective and gets depressed easily. I worried that another male would be bad for him, but they play nicely and they are buddies now. Then when Jimmy came Harley had a problem with him. No aggression, but you can tell that Harl doesn't like Jim. He is getting over it slowly. Plus I think part of the problem is that Jimmy isn't neutered yet and everyone else is fixed already. They know he's different. Plus he acts "weird" because he was a badly abused stray.
Long story short, they are working out their differences over time.

Your guys are pretty young like mine, so they should have no problem accepting a new guy (my opinion). The only problem we have is that Morty is only 1 year old and the energy level is a lot different. Your two might get frustrated with the new guy because he will probably want to play all the time. All of it can be worked out over time. You’ll never know unless you get him. All “packs” are different.