I don't know how to explain this to my family

This christmas year i didn't get anything for my mom's (diseased) side of the family because well.. we can't afford it. I wanted to buy something with my own money but my step mom said that it wouldn't be a good idea because my dad would feel bad since he can't afford it and stuff. Mt step mom told me not to tell anyone because it's embarresing for my dad and that it's not nice. I kinda agree with her. It's no one else business to know too. I really don't know what to do or how to tell my mom's side of the family that we didn't get them gift. I was just thinking to tell my cousin that im sorry but we just can't afford it right now. I'm sure she'll understand, right? ughh, This is just not easy. What do you think I should do?