StepSon touching my daughter in appropriate Places?

I was walking to my step sons(13) bedroom and i came in, my daughter(8 years old) was laying on his bed naked she was giggling and i was panicking walking to see what they were doing but my step son had clothes on his hand was on her and on her private parts she was giggling i walked slowly back to the door non of them saw me and i told him tea was ready and i saw him jump up and run i pretended i didn't`t see anything and after tea i was giving my daughter a bath and i asked her a question "What were you doing with your brother" ... "We were playing a game" so i asked what type of game she told me well i had be naked and lie on his bed he told me we`re going to learn the body parts of a girl and he started doing this demonstrating what they were doing... But i was horrified i tucked her to bed and had a chat with my step son but he shoved the door the door into my face every time i tried to get in so i left him but im still very concerned as soon as my husband came back from home i told him he was horrified to... but i don't care about being horrified right now im wasting my time on the internet but ive tried ringing the doctors in case they weren't open till monday so i`m stuck i came on here to find a good awnser please no horrible answers....