Is this a fight, or just bullying?

 
Hi all,
I have two banggai's, they are in the same tank for two weeks. I think they are wild, cos not taking any dry food. Small one started taking dried  krill last week and for two days ,  been feeding them with freezed artemia and they both go nuts for it.
 
Problem is of course here sexing them. The small one has clearly two vents, but for the big bullying one i can not definitely decide. They are hanging around seperately and the big one is showing his side and jaw to the small one.
 
I 've read that two same sex start fighting to death immidiately. So wanted to ask you if these are both male and which one shold i take back to the store, big dominant one or the krill eating small male?
 
Regards,

Some photos...