here is a link to SSA's publication on being an individual payee.
http://www.ssa.gov/pubs/10076.html
There are some special rules that apply when you get a lump sum including how long you can keep it before it has to be spent down.
Unless difficult child has medical expenses not covered by Medicaid - mainly durable medical equipment, dental and eye care, he should only have minimal medical expenses.
Is SSA requiring him to have a payee? If not, he can dump you whenever he wants and you have nothing to say.
Our difficult child 1 has been on SSI since he was 18. Here is my blunt advice:
Do not be his payee. Instead see if you can get him to agree to transfer to an institutional payee in your area. If you live in a small town this could be difficult. If you are in an urban area or city it will be very easy.
If he won't agree then you can tell SSA that you refuse to be his payee and they will deal with it, assuming he is required to have a payee.
If he is not required to have a payee at this point, I would tell SSA that you believe he needs a payee and why in specific detail. They will investigate and may determine that he is required to have a payee.
Reasons to do this:
1. Reduced friction between you and difficult child and other family members over how his money is spent, when it is dispersed, etc.
2. You are required to report changes to difficult child's situation that may affect his SSI payments. You are almost certain to find that you are in an awkward position pretty quickly. Legally you are on the line if you make the "wrong" decision and SSA finds out. Do you really want to be in that position?
3. If he moves into a living situation you feel is bad for him (for example with his mother) and wants you to pay his "rent" to this person (in whatever amount that person says) what are you going to do?
4. He (or others) can accuse you of misuse of his funds and it will be on you to defend yourself to SSA. This may be harder than it sounds.
In our experience, an institutional payee is a very effective way to deal with the kinds of issues you are concerned will arise without you having to be in the middle.
An institutional payee has everything set up already so you don't have to set up a separate account, etc. They know all the rules and deal with inappropriate requests from payee's all the time. They don't take things personally and they don't argue with the beneficiary. They just tell them no. A good institutional payee will ask - where's your rent bill? where's your utility bill? No we're not going to give you $500 all at once at the beginning of the month, we'll give you $125 each week on Wednesday at noon.
You get the idea. They provide structure without telling the beneficiary what to do with the money they have left after paying for shelter.
If you have a pretty good relationship with difficult child I would ask SSA for a list of institutional payees in your area and then call some of them and ask how they operate. Do they question the beneficiary if he doesn't bring them bills to pay or if the bills seem outlandish? Do they split the money up for food, etc so he gets some every week instead of all at once? What is their procedure for transferring from a private payee to them?
Then go check out the best 1 or 2 to see how easy it will be for difficult child to get to them, what kind of area it is - is it a safe area for difficult child to be on foot with cash in hand? Stuff like that.
Once you've settled on one or two then I would talk to difficult child and take him there to check it out and talk to someone. If possible get him to sign the forms right then to have them made his payee.
Finally, keep in mind that if biomom or anyone else swindles him out of his SSI money they can be reported to adult protective services for abuse of an incompetent adult and the problem can also be reported to SSA to help reinforce your difficult child's need for an independent payee.