This is pack hierarchy exercising itslef, and is perfectly normal.
In any pack situation - which is two or more cats, one or other will try for the 'top cat' position - first feedling, best place for a warm, and so on.
Usually, eventuallly, the more determined cat will push for his status - that's the growling and spitting, and similar 'come on if you think you're hard enough ... behaviour and the other cat(s) will agree, and step down the pecking order, and peace will resume.
If however any other cat(s) are not ready to give up their potential top spot, they will fight for it, until they either decide to give in, and let the other have his way, or push until they win, and the other cat backs down.
All you can do is leave them to it. This is perfectly normal cat pack interaction - they will sort out for themselves who is going to be 'in charge' and that will be that. You may not notice any serious cahnges in behaviour, but they will be happy knowing their own place.
The reason why this has started now is that your cats are growing into mature males, and the hierarcy kicks in, and they sort it. Don't interfere, it's nature's way.
Hope that helps.