I see things somewhat different in some points. Not about that spaying is a good idea though, for many reasons, especially for free roaming indoor rabbits. All this hormonal behaviour can make life difficult for all involved. Cancer is a serious risk, although that 80% number is a somewhat blown out of proportion deadbeat argument, but even if it's just 1/3rd of that it's still not worth the gamble.
For a long time I had 2 pairs of intact does, now, after Fury died I'm working on getting the 3 does get along. Red got spayed at 7 (due to a stuck kit), but that didn't change her behaviour a bit. My other spayed doe, Dotty, which lives with my buck as free range house bunnys is the most territorial and aggressive (to any other rabbit than Pacino) doe I have, The second another rabbit gets into the front yard it's an instant Furnado.
Rabbits are social animals, and does are often able to get along, they are good in sorting out their hierachy, but getting used to each other can take time and may be hard to watch, read up about bonding. My impression is that many meddle too much, break up everything they think is aggression, and chosing wrong location and setup.
Imo hormones are more prone to make life, hm, "interesting" in the long term than messing up bonding directly, although they definitly don't help. Character mismatches are possible (that's why I had 2 pairs - 2 dominat alphas didn't get along), but I would guess that in the single digit percentage numbers, not 99%. Spaying is not "cutting them back to behave" and implanting social skills, character doesn't really change that much.
Did you already try to put them together? How, where?
My approach is that my pair and my now single doe had their own, fixed, unchanging territories, and then I started to connect them, first small openings, then removing more barriers and adding a connecting tunnel between the hutches. I did not let them use the same spaca alternatingly, that for sure would cause an instant territorial reaction. I also think it's important that they can get out of each others eyes when they feel like it, or if there is an disagreement.
I cheated though, so I can't tell if my experiendces are representative - Ruth had a litter 4 months ago and at first I made the openings just big enough for the kits, they got Red used to the idea that there are other rabbits around her, a whole herd made things easier because they don't focus so much on each other, I will keep one of the doelings. Also mine have lots of space, now 5 connected hutches for the night, and 200m² garden even when they are not out on the meadow.
