I keep my 2 billies together. they can be run with the nannies or separated at breeding.
iv had no issues. they do play fight but had no injuries.
now mine are mature, the size of their horns (we have bagots) means the housing needs to be larger if they are sharing a stable. if they do fight, they are very tall also so a standard stable is a bit small now as you need space for them to escape.
depends on your set up, and I suppose they goat as mine haven't shown aggression to humans either, where as some billies do.