<human>: Give me a shortened version of the text

I'll try to keep this quick.  Visited an uncle and aunt a while back. During my stay my uncle patted my ass once with a paper program while we were at a show (in front of people).  Too shocked really to do anything, but exclaim in shock.  Then later, as I was putting away dishes while they were both watching (some awkward television I removed myself from) He came into the kitchen to tell me I didn't need to put the dishes away.  I said I didn't mind and he then gave me a hug in which his hand strayed to my butt.  Nothing lingering, just the totally wrong area for a hug, you know? 

I'm pissed and freaked out because I have history with this side of family.  Mostly my father (uncle's brother) disowning for a few years, because my job might be a bad influence on my young sister... (I worked in the sex industry, my sister did NOT know, and I would never tell her.)  But I wasn't allowed in the house for fear of tainting his new family (he remarried and had some more kids).  

Now this sister, who mean the world to me, is visiting this uncle with her parents and I don't know what to do.  Do I send an firm email to my uncle that his actions were inappropriate and he should stay the hell away from my sister.  To their mother (my stepmother) or my father acknowledging uncle's behaviour.  I'm worried that my father would accuse me of lying and disown me again.  Or my uncle will deny it and the email trail will look like I accused him out of the blue.  But I don't want my baby sister to have to navigate pervy uncle bullshit.

This is really fucking with me and the potential can of worms is frightening me.  There is no guarantee he will do this with her.  I saw him occasionally growing up and didn't notice/remember anything off... but still.  ew.
<bot>: pervy uncle touched my butt, younger sister visiting him this summer.  Who do I tell to make sure this doesn't happen to her/anyone.  My family already questions my moral fortitude and may not believe me.