my husband treats my kids different to his kids

so we are a blended family. he has 2 i have 2 and we have 2. his daughter is 10 and is pretty much a good kid aside from the normal pre teen outburst but his son is the golden child. hes 8, kicks his older sister in the croch, talks about killing people, doesnt listen to a thing thats asked of him, talks to me like i am a child and is an absolute pain in the ass at the best of times. My 6 year old is very sensitive and cries a lot and is a bit of a full on drama queen and i can admit this but if my step son is kicking his sister in the vagina and swearing and being a full on shit my husband will be like "come on buddy, please dont do that." in this calm kindergarten teacher voice and when my child acts up he uses a more stern voice and calls her "ungrateful" and "toughen up princess" ... I am honestly getting sick to death of sitting back and seeing him treat them differently. I told him he treats his son better than her and he said "oh well" ... or will say "no i dont" .... it makes me really bitter toward my step son because i dont understand what makes him so much better than my kid. i feel i treat them all equally buying them all bday presents and stuff and he doesnt buy my kids a bday present even... idk ....