This is more common than you think, I've seen it. Senior parents want to help their adult children but either won't accept or understand enabling. Older adult children addicts are just as bad as a teenager trying to manipulate, scam, fool parents.
As mentioned best bet if they really press the issue refer them to the estate lawyer. In most states the money can't be distributed to heirs until the estate is considered closed. Unless it is from an insurance policy or as a pre-designated beneficiary of a bank or brokerage account.
It probably wont end there. Several years later the addict is trying to get others to put them on their car insurance or use their address for cheaper auto insurance because of dwi's on record.
Good luck, stay safe!