My brother is 93 has Navy Pension and his S.S she was getting both and not paying anything, she moved to Sweden Nov 2016 still got his money. I stepped in late Nov 2016 was far from easy to change things around even with POA I took my Brother to S.S so he could change Direct Deposit so he did and got check Feb 3rd. I wanted to be sure he be getting his check for March 2017 but he isn't getting it at all ok ,Feb 9th someone changed where check should go on line now he won't get his check. Now to stop March 3 rd check how. whit her not paying his bills he's 5 months behind in mortgage.
Sounds like "she" has set up an on-line account with Social Security for your brother and any time the direct deposit goes elsewhere, "she" is able to make the change back to where "she" wants the check to go.
You need to call Social Security and explain what is going on. Maybe they have someway the on-line account can be locked after the correct direct deposit location is set.
Do the same for his bank accounts. Sit down with the bank manager and explain the situation.