Hey there! Kudos to doing research before just jumping in and trying to bond without researching about Trios!! 

Trio’s are completely different dynamic than Duo’s because there’s an additional personality and presence to get used to! Also, i would wait a month after Marshmallow’s neuter (if i hasnt been a month already) so that his hormones drain completely and they aren’t all wacky.

There is a thread from Sirius&Luna who is bonding a Trio currently, i would suggest checking that out! Here is a link to it: https://binkybunny.com/FORUM/ta…fault.aspx . So far, i think she has been successful!

First thing’s first! I highly recommend starting the pre-bonding process, this gets everyone used to each others scents and makes them less likely to be aggressive or territorial towards each other. 

Pre-bonding typically consists of swapping litter boxes with another bunny’s, switching cage trays, and toys/items like stuffed animals (without glass/plastic eyes or pieces attached to them) or fluffy socks (i’ve been giving my bunny one to snuggle with )

After this, start the introduction process! The easiest and most popular way to do it would be introducing each other in pairs, so lets say you start with Milo and Marshmallow. Bring them to an absolutely neutral territory. This could be a coffee table, like Sirius&Luna have been using, or just somewhere none of them have been before (thats safe for bunnies of course lol). 

Always start out small, so start with 5 to 10 minute sessions (I would recommend 5 minutes for the first week)
until you see no signs of aggression. This means no grunting, lunging, nipping, and absolutely no fighting. If fighting occurs, separate immediately and try more pre-bonding. 

The whole bonding process including the pre-bonding would take about 2 months minimum. So be super patient and encouraging to them! 

If you need more information, which i would suggest, there are quite a few posts about pre-bonding that wouldn’t hurt to read! I hope everything goes smoothly, keep us updated!  Here are a few to get you started! I hope they help, please feel free to ask more questions if you have any!! 

General bonding and pre-bonding information page: https://binkybunny.com/BUNNYINF…fault.aspx

Mikey’s Trio bonding journal: https://binkybunny.com/FORUM/ta…fault.aspx

AnnaW’s Trio bonding journal: https://binkybunny.com/FORUM/ta…fault.aspx

Bianca’s Trio bonding journal: https://binkybunny.com/FORUM/ta…fault.aspx

Onyx has given you pretty spot on advice!

For prebonding, the easiest way in my opinion is just to switch them between cages. So since you have three separate buns, it might mean leaving it a bit longer between hutch cleanings than you’d like, but it’s for a good cause!

The other thing that really helped mine was sharing a room that they had their (separate) free roam time in. It’s my living room, and it has now been covered in territorial poop and pee for 4 months (obviously I clean but I mean they’ve been consistently marking). So they’ve all smelled each other, and I think they came to the realisation that it was shared territory, since weirdly, that was the space where we had the bonding break through.

I really do recommend reading some of the bonding journals that Oynx has helpfully linked to. It really helps to see what stages bonding often goes through, and to understand positive and negative interactions, as well as giving you some new ideas to try. Often, if the bunnies don’t seem to be getting on, something really simple like a change of scene, or sitting in there with them can totally change the dynamics.

Honestly, that’s what Luna was like at first. She would immediately lunge at the boys, and if I stuck my hand in front of her to stop her, she took a chunk out of it (obviously meant for the boys). She was very very stubborn, and sounds a lot like Mitsy.

I know its annoying when she pees and poops all over the cage, but that’s kind of the whole point of it. I think if you persist in that, eventually she’ll stop marking. If the boys immediately lunge for each other too it’s another sign that you need to do more prebonding. Where did this happen? Was it neutral space? I would definitely spend another month switching them between cages. I know it’s hassle, but it’s the most likely way to get them to tolerate each other.

It’s unlikely that they’ll be able to share a free roam space but not a living space. Generally with bunnies it’s all or nothing. Either they’ll fight and not be bondable, or they’ll be able to share the space and you’ll be able to fully bond them and have them all live together.