My mindset on this is that bucks sold as pets should be sold in pairs only. I say this because the theory is, that one male will be dominant and one will be subordinate and as long as he knows his place, the two brothers should get on. There are guidelines that a new owner MUST follow though and these are:
1. Make sure both males live in a the same cage all their lives.
2. Never do full cage cleans with males. Keeping back half the substrate/half the bedding is essential. Males do not like change.
3. Only clean one cage toy/accessory at a time, or give throw away items like cardboard tissue boxes, egg boxes and toilet roll tubes.
4. Have TWO wheels in the cage to prevent arguments.
5. If one needs to see a vet, take both along. Never split males up unless it`s only for a few minutes here and there.
Most importantly, anyone keeping a pair of pet males should have a spare cage ready.
That`s the main points really, so anyone taking on two males should be given a caresheet with these instructions, especially if they are new to keeping mice as pets. I started out with four males, learned the hard way, had to split them into one pair and two singles, yet my boys were all loved and played with more than most kids are! So as long as they are prepared to take that on, males are wonderful!