Hang in there Danaiglu and good on you for supporting your SIL. :-x

Sorry, I have no advice other than to keep asking.

As for Dad being in denial, that is all too common. 😞 People don't want to have a child with difficulties - it's too scary. It also may be scary because autism (if that is your nephew's problem) can be hereditary and some parents don't want to contemplate that they may have it too.