Me and my sister’s buns are those same ages, mine is 3 months, hers is about 5 months. They both really like each other, they like to snuggle and run around together. I think they should bond easier the younger they are, and since you are desexing, they might bond even easier as they won’t have raging hormones.
Unfortunately, me and my sisters buns can’t live together as we’ve recently discovered that my sisters bun is actually a boy, not a girl like we originally thought. We let them together under close supervision.
You might not be house them together on the first day you bring home the new bun, you’ll need to bond them in a neutral area neither bun has been first, like in the bathtub, and see how they like each other. It’s just that if your first bunny finds a stranger in her house there could be territorial fighting.
Good luck, and I want to know how it goes!
P.S. What do they look like and what are their names?