Can I be held responsible for someone's past outstanding debts if Social Security Office appoints me as to take care of his finances?

You are absolutely NOT personally responsible by virtue of your helping him pay his bills. God bless.

I say no but you should think of moving him to a new place I am not sure they should get all but 35 a month from his ss what did he have in bank before you took over helping him and what dose what did he owe them interest not included sub tract that it is bal he should have now what dose he pay a month to them subtract from as monthly take old bal and new he should have that in his ck account

You cannot be held responsible for his debts, however, he has to be competent to answer questions at Social Security IF you want to become his Representative Payee. If you are appointed, then you have to make a yearly document as to where the money went. This is different than having a POA. Social Security does not recognize a POA.

The nursing home routinely charges a person's whole check, less the small personal allowance. The personal allowance is for his use, personally, not debts. This can be paid directly by social security, but that is obviously unwise in this case with the DOJ involved. If you are writing the check, and you have POA, be sure that you are also assigned rep-payee by social security. Open a separate account for him. If you want to preserve his dignity, ask him if this looks ok, I have signed it for you, etc. Of course you are not responsible for his debts from your own finances. Always keep your finances separate from his. Always keep records for soc. sec. Always act in a responsible fiduciary manner, in his best interests. Social Security has written instructions for rep-payees, either online or at the local office. Go there. Take your POA documents, the doctor's note saying he is incompetent to handle his financial affairs, SS will assign you as rep-payee, he wouldn't have to even be present. If you keep allowing him to sign checks for his own account, what is to prevent anyone else from having him sign a check for them? A fiduciary doesn't just write the checks, I'm sure you are aware, the entire financial picture is protected and managed by you. Does he have family for the medical issues?
Would you be able to take on the huge responsibility of medical decisions? Looks like a transfer to another NH is in order?
As for the NH debt, get him signed up for Medicaid, if he is not already. A NH has a number of designated beds for Medicaid, put him on a waiting list, find him a NH with a Medicaid bed, it should cover the retroactive debt with the nursing home, Imo. Maybe that is why the DOJ is looking into this NH. Is this SS his only income and asset?
Here is a note to all those caring rep-payees out there: A rep-payee is only responsible for managing the SS income. You need a POA for other income.
This may be handled unspoken for awhile, while the patient is cooperative with you. But there may come a time when your hands will be tied to help if you don't also have POA. I'm just guessing here, wish I was an attorney.

Ok. If the one and only bill became past due, what happened to the funds for that? What was the NH expense spent on? I as a rep-payee, do not pay anything without a statement or bill. What extra funds are you/or he paying the NH debt with? That seems irregular in some way. Are you using co-mingled funds as his partner? You don't have to answer in detail if you are not comfortable, but caregivers gave answers based on the relationship as friends, not "partners" as in could possibly be common law marriage, in which case, the law is different.
You cannot use the $35 personal allowance for debt. See an attorney if you have shared finances over the years. Does he have a will, instructing you to pay off his debts with assets? Then, yes, you will be held responsible out of his estate.
Don't get afraid, take care of this with the right legal advice and financial planning.

I would think it is time to get a lawyer who is up to date on California law. My mamma is in a memory care unit in NC and because of new medicaid laws she can never qualify -each state requirements are different. Don't wait until person is incompetent to make changes and this can happen really quick. Good luck,in what can become a nightmare if government is involved.

Our personal lives do become nightmares when the government gets in to "help". Giving with one hand and a set of rules no one can follow or interpret, and taking away with the other hand. Keep being independent, even fiercely independent, even when our adult children want to help by sending us away. In my never to be humble opinion. Disclaimer: Caregivers on this forum are really here to get and give answers, they are special people who have helped their elders. Some have even taken on the financial burden themselves, when able.