Cockerel on right
Spurs don't usually begin to develop until after 6 months of age. Some roosters never grow spurs, and some hens can grow spurs. It's not a reliable way to gender a chicken.
Yeah I suppose that is true... kinda forgot about that, thanks for correction!
Males that are raised together will develop their own pecking order. There may be a few fights as they mature, but it shouldn't be too serious. If you've got one that just won't back down and is constantly starting fights, it's not normal. That is an early indication of a male that is going to be too aggressive.
I'd suggest keeping a close eye on them. I had two brothers that were fine together (free ranged with the rest of the flock) until one day (around 3.5 months old) when the "young pretender" decided he wanted to be top dog. Within 10 minutes they had caused serious injury to each other - it came out of the blue (to me at least). Be prepared to cull any nutcases as aggression is not a desirable trait for breeding or you own safety.