Local Authorities are well up with all the tricks that schemers like your BiL think up. They can, if necessary, get information from HMRC, who get information from all financial institutions in the country and will check whether your DM has had money in any saving account, which has now been closed and the money distributed.
Put simply if money has been given away or spent in order to avoid it being used to pay for care the LA will simply do the calculations as if she still had the money. At 92, it will be very difficult indeed to prove that money disposed of was NOT done with the intention of avoiding care fees.
I used to be a Case worker for a charity for the elderly. None of the schemes you BiL has thought up are originally, in fact they are the methods the majority of small time avoiders use. They do not work. The financial investigators in the LAs are well aware of them and will find them out.