It's very possible for stallions to live together without problems. Wild horses do it all the time in a bachelor herd. But, there are some stallions who don't get along with other males too so it's based on the stallion himself whether he'll accept the other geldings or stallions in his pasture. Some prefer to be with their mares and foals. The situations just have to be monitored closely. Stallions can get along with them one day and the next he's chasing them through the fence or worse.
The one colt(now gelded) my grandma had was with a gelding even after he knew he was a stallion. They picked on each other, but nothing as far as killing or chasing off. Just typical herd boundaries of dominance. He was penned close to the mare and gelding pen without problems between the stallion and his buddy. In fact, they were full brothers born on the same day two years apart. Same color and nearly the same markings to a degree. The only way to tell them apart was the stallion had a flaxen mane and tail.
Then with the same two horses before he was gelded we ended up with a visitor somehow. A welsh type pony stallion in the pen. Besides loosening the fence, no real damage. Both stallions got along. The gelding was jealous of the new pony. We just woke up and found him in our pasture.
Here are a few pictures. The bay is the visitor stallion, the sorrel flaxen is the stallion, now gelded. The pony's owner came by and got him. No harm to the horses and the bay was just a friendly horse. SOX.jpg SOX N PONY.jpg