They may get friendlier as time goes on, but bear in mind that in their normal state cats are solitary creatures, 2 brothers together since birth is a different matter, I kept a mum and her son together for 16 years and mum hissed and spat at him whenever they were in the same room, again if you think that left to their own devices the kittens when old enough would go and look for their own territory and this is the reason cats often don't get on, they are very territorial even at this young age, he has established his territory, though he is and hopefully will be young enough to adapt.
Good luck.