The government won't automatically stop any SS checks if someone is missing. It's up to the guardians to be honest (not spend the money/notify the government) or they risk fraud charges later and will have to repay it. And I didn't necessarily mean family members. There could also be nurses or other home healthcare workers who might still be getting paid even through they are not making visits anymore. The healthcare workers should have reported that they stopped seeing the person when they went missing and the payments should have stopped, but that doesn't always happen. See Carl Debodie's thread for an extreme abuse case where workers profited from covering up a disabled man's death:
Found Deceased - MO - Carl DeBrodie, 31, Fulton, 17 April 2017
In a nutshell: They had an illegal fighting operation in the basement where they made disabled people fight each other. They left Carl to die on a cement floor from his injuries and didn't get him any medical help. Then someone put him in a bin, filled the bin with cement and put the bin in a storage unit. His death was not discovered for months. The people who were supposed to be caring for him kept collecting checks.
Back to Joni and Brian-- they seem to be mostly independent (had their own house) but if they both received disability payments they might have money coming in or some money in the bank.
It could be a caregiver scam like Carl or someone who weaseled their way into their lives, pretending to be a friend in order to gain access to their bank accounts. Hopefully LE is on it and the person responsible won't be walking free for long.