step child woes

So my step son has a nasty attitude he is 4 next month. my son is 2 next month... they are brothers we try our best to treat them the same..BUTTTTTT... my step sons attitude makes me uncomfortable bc i don't feel comfortable correcting him the way I correct my own child. he says things like "I'm not talking to you" and "where's my food" "why aren't you making my food" not as in innocent question but as in literally why,are u here without my food lol. now if my son talked to ppl like this I would tap his mouth and tell him no you don't talk to ANYBODY like that that. step son his father does say don't say that his grandma also says don't say that say it this way.....nothing as changed so I've come to the. that I now ignore him unless it's an emergency or he specifically calls me name asking politely for something other than that I just ignore him bc I can't stand it and I'm upset my son will pick it up....I have been amazingly lucky that my son has picked up ALOTTT from his brother but not that. Am I wrong for feeling or being this way? what can I Do? I've tried talking to him but the disrespect has made me shut down bc I want to spank him but can't bc like I said if it were my son it would have addressed strongly and corrected