I dont know how to talk to my boyfriemd about this but .. when our son comes im not sure to give him mine or his last…

I dont know how to talk to my boyfriemd about this but .. when our son comes im not sure to give him mine or his last name BECAUSE .. his last name is baez but he wants to change it to his moms which is gonzalez .. but he keeps holding it back and hes not sure if he wants it gonzalez or sanchez .. sanchez is his STEP dads last name and i dont want to be mean but i dont want my baby to have his step dads last name .. one is hes really rude to me , he threatens to take my son when hes here , disrespected my brother in the marines, disrespects most of MY family and im not sure to give it gonzalez baez or mine which is garrett and i really do not want is sanchez .. my boyfriends not sure if hes changing it or not and if he still has baez od give him his moms last name or mine but then i wouldnt wanting him to change it to sanchez cause then his son wouldnt have his last name ... sooo any tips on how too talk to him about this ?? or on what i should do ?? feel free to say what you think it should be or what i should do ??