I need help w/ family trouble?

k my parents r devorced, so i live w/ me mom so she doesnt talk about my dad alot. so my dad got remarried & he invited me 2 the wedding & not my mom. so now i have 4 half siblings. but i dont get along w/ my stepmom dat much, so 1 time i was watching court on tv i thought dat the women looked like my stepmom, it turned out it was here. she had hidden tons of bags of drugs in her brothers house, i felt shocked. ive never told anyone, she got fined. the next time i saw here i felt so weird & uncomfortable. should i tell my mom or not cause if i do she may not let me see my dad & my siblings ever again. plz help me.