I had 2 bantam roos that were raised together. They got along, and slept together cuddled in a big ball. At about 3 months old, the bickering started. I figured they were establishing their pecking order and since they didn't have spurs yet, they wouldn't really hurt each other. But the bickering became real fighting and it was constant and bloody. If they had their spurs grown in, one of them probably would have died. After a few days of this, I decided to get rid of one of them to keep the peace. One was a d'uccle and one was a cochin, and these are supposed to be pretty docile, especially the cochins. And I must say, both of them were always extremely sweet and docile with us humans.
This is just my own experience and it's possible that if I had given them more time, they might have worked it out, but I couldn't take it anymore. Some have kept multiple roosters together with their hens just fine, but you should always be prepared for the possibility that it will go bad. It can happen fast and unexpected.
As far as bantam roosters being more or less likely to get along than standards, I don't think it makes much difference. If anything, bantams are generally more high strung than standards. And for a gentle breed, Bantam Cochins are well known for their gentle, calm nature. Mine was very sweet - gentle and calm in every way, but still had the built-in instinct to fight the other roo for dominance and be king of the flock.
However, it's my understanding that most roosters kept together without any hens generally will do well. It's when they have hens around that they will fight.
I have 3 dutch bantam roos. 2 are brothers, the 3rd is a week younger. Now they're over a year old. they show off in front of each other, but i've never seen them fight. they are the friendliest roos. i walked all over the place with any of them. i also have a full grown leghorn roo that is the alpha roo of the flock. maybe he keeps all the little guys in line.
We had 7 young bantams given to us. All but 1 were supposed to be pullets. Turned out that 4 were cockerels and only 3 were pullets. The cockerels "play sparred" every day but we got rid of them before they got old enough to do any damage. They were brothers.
When we got 2 barred rock bantam hens, we added the barred rock rooster soon after that. He is extremely gentle and was handled a lot too by his previous owner. We'd originally decided we didn't want the rooster so just took the hens home. We changed our minds and when I called the lady that had the rooster to tell her, she was happy because he'd missed his girls and had went out back and had been fighting through the fence with a standard size rooster. Now he's happy with his 5 gals.
If there are no hens around, they usually won't fight, because there is nothing to fight about. I have a friend who houses his 6 or 7 roosters, all different breeds, in one coop, without any hens. He has never seen evidence of them fighting.
I have been under the impression than bantam roosters are a little less aggressive and more tolerant of other roosters, as compared to standard sized roosters. My own experience tends to support this, but this is based on a pretty small sample size, so I cannot say it is fact. I currently have 2 bantam Brahmas from the same hatch, a little over a year old, who get along well with each other housed with a bunch of hens. One is dominant over the other and seems to "possess" most of the hens, while the submissive one "owns" just a few of them.
However, each will sneak mate the other's hens. When one catches the other mating "his" hen, he will not attack - he simply mates her himself immediately thereafter. It can look like gang rape and is probably not very pleasant for the hen, so for that reason I am constantly considering getting rid of one rooster. Also, just because they get along well now, doesn't mean they won't suddenly start fighting one day....Like maybe when the dominant one gets sick or something, and the other one thinks he can defeat him.
I have another friend with 2 dutch bantam roosters, also housed with a bunch of hens. She has had them for years and they never fight. One seems to accept the submissive role and, as far as my friend knows, never mates any of the hens.
And, of course, the more space they have, the more likely they will be to tolerate each other. I think if they are always confined to a small space with a bunch of hens, they are more likely to fight. If the flock free ranges all day, the roosters are more able to avoid a nasty conflict.
Certain breeds seem to have a reputation of being more mellow and tolerant than others, with the game breeds obviously the more belligerent. Brahmas, cochins, and dutch are sometimes rumored to be among the more mellow. However, there seems to be a lot of variation within a breed (at least in my own experience), so I wouldn't hang my hat on any of that. If you confine 2 or more roosters (any breed, any size) with hens, you take your chances.