I see....it is part of the manipulative nature of addiction. "You see...how I can be trusted when I tell you about the money that I have.....now can we put it in your account. I need it now!" If he had another way to cash it...he would have I suspect.
The active addict makes you feel crazy even though you are the lone wolf of sanity.
Helping him obtain money, in any way, is just fueling his addiction.
If there is no benefit to your daughter or grandchild by helping him...then I would stay away from all transactions and contact.
So sorry your family is going through this....