Fifteen yo old family member told and showed 9 yo and 6 yo sisters how to masturbate. She placed a pillow between her legs, told the youngsters to pretend its a boy and proceeded to hump it up and down , saying "until pee comes out". The 6 yo didn't understand, laughed and mimicked. The 10 yo whom only knows "the penis goes into the vagina" when it comes to sex ed, but not erections and ejaculation, grew very upset. She left the empty bedroom and went to basement where teen and sibling followed. Teen then made them play truth or dare with would you rather have sex with a boy or kiss yoru sister on the mouth. Again, youngest doesn't understand sex so laughed but 10 yo again upset and wanted to leave. Teen proceeded to to lift her shirt to show bra and cleavage, trying to get them to do the same. 10 yo when relaying this, said teen has shown bare breasts to her before. Again, 10 yo wanted to leave the situation but didnt' want to leave her sister alone with the teen. Teen apologized and begged 10 yo not to tell (showing she knew it was wrong). Teen is aggressive and threatened 10 if she told anyone. Teen is obese and was in a pseudo-babysitter (adults in home not checking on them obviously) of power. Teen is six years older than eldest child and nine than the youngest. When finally separated, the 10 yo did not tell any adult in the house. She was afraid to get in trouble. She feel stuck, because she knew this was all wrong but was afraid what her sister would experience if she sought help, at the time. 10 yo needed lots of hugs and reassurance. She asked to speak with her therapist (suffered previous d.v. trauma) who is on vacation and she doesn't want to talk to a different one. She does not want to talk to the school psychologist. Even without touching or nudity below the waist, given the age difference, much larger body size and the 10 yo victim's reaction, I consider this abuse. Now the complications. This happened while on court visitation (with a grandparent, this is not a nasty divorce situation). The grandfather thinks this is all hilarious and wont agree to keep the teen away. Teens parents both work for our small town. I dont know if they even know what happened considering the non-concerned reaction from the grandfather/uncle.Would you call social services? File a police report? Try to get a court order that teen is not on visits? Be both ticked and sad they experienced this? This was not a one time thing, though both declared as the same time. If they were all the same age, I wouldn't like it but agree it happens. For all the reasons already mentioned, I do not feel this is a curiosity thing. Also, the teen volunteers at a preschool, which is another reason I dont want this to be swept under the rug. The 10 yo has the right to feel safe and will heal but I dont want this happening again or worse, to her or any other children. Suggestions?