cockadooddle I will grant you that I did add 'despite what he did' but I meant it as a way of explaining why the SIL's previous behaviour may have appeared contradictory and given no sign of being uncomfortable with her Brother being around her children bearing in mind her viewpoint position.
I did add that the SIL could be lying, albeit the possibility being small.
I see no misandry on this thread. This is not a debate about the propensity of women vs men to abuse children, and the accused here is male, so your accusation is unjustified.
Re: my emotional bias. You clearly have bias of your own. The o.p. had trouble understanding why her SIL would continue to allow her children to be looked after if what she was saying was true. I sought to provide some insight into how such seemingly contradictory behaviour can occur. I stated that it was a complex issue for the OP to get her head around, and should therefore be looked into by CSA trained social services or the police, who contrary to what some have said, are not all incompetent, despite some high profile failures.
Perhaps I am biased in the one sense that my experience means that very little surprises me in cases of CSA. My SF for example was considered a generous, funny, warm, man who 'liked the ladies'. No, he liked kids. He raised money for the community hall and drove a community bus for the elderly. He was great with my friends who he never attempted to molest bar one, who cut me off and moved away to live with her older sister, to get away.
I perceive sexual abuse to be such a secretive crime, as secretive as say, a fetish for extreme porn (I am not trying to equate the two, merely point out the futility of being able to tell who could be a SA) How can you tell from the outside what a person thinks?
The best thing the OP can do is speak to her sister-in-law, but barring that she is in a very difficult position. I would not blame her for not wanting to rock the boat, especially as no official charges have been brought.
OP I apologise if my post was unhelpful. Sorry this situation has turned your life upside down.