Yeah, it's hard to give up those cute babies when you raise them and get so attached. I only rehomed one of mine and kept the rest cause I worried so much about them going to good homes.
Some people will quarantine for a month, just to be safe. I've gone both ways. I quarantined the stray my neighbor found, for a month, but didn't on a new baby I got because I was worried about the stress of keeping her separate and alone. There's always a risk if you don't quarantine, but there's also nothing certain that a month is even going to be long enough for some things. I've found it's mostly breeders that will quarantine new rabbits. Usually pet owners don't in part because they don't think about it, they are keeping the new bun no matter what and these buns are going to be sharing space any ways, and sometimes it's just not feasible to quarantine.
I would say if there is no chance you're keeping him, then it's probably best to continue to quarantine. No sense in risking the health of your own buns. But if you are going to keep him for sure, then no reason not to introduce him to your buns. And if you do introduce them, first see how they react through cage bars. If there are signs of aggression, you probably don't want to let them be together until they've had a while to calm down and feel more comfortable with him, or until he is neutered. If they just seem interested in each other, you could probably very cautiously introduce them, maybe with Papaya first, as he seems like he would be the most easygoing about it. And just watch for signs of aggression or irritation(tail up, circling, lunging), and end the intro if there is any, before any nipping or biting occurs.
Some people say to wait until a bun is neutered before introducing them to each other, and in some cases you do need to do that, but I've had times where I have needed to put a baby bun in with an older one, and it's worked out well. I carefully pick which older bun, as some aren't friendly(Dakota
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), but there are benefits to letting them be with an older rabbit. They can teach them bunny manners and also give them a friend, and help them not feel so nervous in a new home. But this all does need to be done carefully, as you don't want the older bun attacking the younger. But I've sometimes found older rabbits will often behave differently to babies than they would to another adult rabbit. They are usually more accepting of them. So you just have to kind of gauge their reactions and go from there. Curiosity and interest are good, tail up and pawing at the cage bars aren't. But you dealt with the difficulty of Kiwi and Papaya, so you know what those negative reactions can look like.
For the weight, not that it matters all that much as long as he doesn't seem boney, but when Baby was 4 weeks, she was really small at 4 oz. By 5 weeks she had doubled her weight. And Baby is part lionhead and is about 4.5 lb now.