Is it ok to return gifts u bouhgt for ur gf kids?

ive been with my gf 1 yr . her 4 and 9 yr old r brats and disrespectful to me and her . i also live with her and knew of thier behavior prior to moving in. i thought i could change things and i cant without drama so ive learned to accept thier twisted relationship. the 4yr old will talk fowl to her and tell her no and what hes gonna do. making his own decisions and we all know 4 yr olds dnt know whats good for them. the 9 yr old is a pathiological liar and addicted to to tv 24 hrs a day except for when he is at school even eats and sleeps to tv. i am not allowed to turn it off. they dnt know it but i spent 150 dollars on them for christmas in front of thier mom. i asked the 9 yr old to take out trash he had a fit and said he hates me and cryin cause he was watching tv. he also scratched up the puter desk today. his mom never confronted him about it. i am fed up with thier attitude and disrespect. i want to retrn gifts and focus on my 2 kids. buy 1 each for hers. is this a normal