Advice please

I need some advice on what to do about my situation. My husband and I have 4 boys . He has one from previous relationship and I have 2 from previous relationship. The father of my 2 kids is absent and lives in another state my boys don’t know him at all so since they met my husband they think that’s their dad . My husband pretty much raised them . My husband told me from the start he wanted the boys to always look at him as their dad and not know about his bio father . The bio father abandoned them anyways so I had no problem w that . Anyways we had a baby together so our family quickly turned into a family of 6 . His son is 5 years old and he’s very smart kid for his age he asks a lot of questions . Recently every time he comes back from his mother house he tells us that my boys are not his brothers but his “step brothers” and he says I’m his step mom . Which Is true but my husband bothered him that he called his siblings step brothers when they should be brothers since they’re raised together and we don’t like to label things like that and his son also calls me by my name we always respect his mother . The other day he can from his moms house again and asked my husband why my son calls him dad if he’s not their dad . And we didn’t know what to say bc my husband doesn’t want my boys to know yet since they’re only kids . But apparently his bm has been telling their son to not call my boys brothers and telling him a bunch of stuff . She has never liked me and I don’t understand what to do in that situation are we wrong for trying to keep things the way they are or is she right for wanting to tell the kid the truth