It would be very much better than doing nothing to go to the extended family who are senior to the rapist cousin.
When I was a pre-teen, one of my grandmas married again, a farmer down the road from her own farm. We little girls found out he was a groper. And it was also obvious he was losing his marbles generally. The females of all ages took it into their own hands to warn every single female cousin not to ever be alone with 'Uncle Bill', until he died not much later.
I don't know how Thai females handle such things, but it occurs to me that this person's mother and aunts are the ones who need to band together and put the reins on Raper Man. Presumably he's not senile, which means he can be reasoned with by females of the family.