2 things: yes it can still be a boy (basiliks are VERY hard to sex on hemipenis basis, even with full growns the diference its not as obvious as it is say with green igs because they lack femoral pores and the bulbes are not very obvious) and you shouldnt be doing that combo wich would only be fairly aceptable in the long term if they were 2 females, if they are a copple they CAN cross breed no doubth about (it has be acomplished several times if Im not mistaken in Germany) and if they are 2 males most likely they will figth. At a foot long it is still to early to sex it 100% sure, you have to let him/her bloom. If you have a male brown for shure and you put this young animal in you are seriously risking its health, why? If is a female you risk stressing her and even a possible early pregnancy and egg bidding (and that putting alone the non advisable cross breeding thing) and if it is a male the other male will treat him like a female, stress him like hell and even stun its development. I would say its better to keep them separeted, get 2 female brown basilisk and wait untill like 6 mouths from now in wich you can sex it for shure.