Looking for advice on what to do?

I am not a legal expert, but I doubt him buying smaller items is going to be considered especially since he has been a caregiver. They could see what money was being used to attend college including books. Internet should be considered a necessity if he is doing online classes along with basic living expenses like food, gas, bills, etc. The forging of the check is going to be the major thing. He can prove he is a student at whichever college he is at, and they can show if he has been attending (if online turning in assignments). Now, if he was going on a spending spree spending hundreds and hundreds, then yes, there could be a problem.

Clearly the grandson did wrong in using the grandparents money for his own things.
Lucky for him, what mess CURRENTLY exists is so much more large than all of that it is truly unlikely that the grandson will be bothered by any of this at all.

Currently the state is the guardian. If grandson remains on anything at all he needs to get his name off of it and explain to bank, etc that the grandmother is currently under the control of the state.

I doubt anyone will come. If they do, then he is best just to admit he had no idea, living with her and caring for her in return for his room and board, that he had to keep track of everything he spent for her, and he did not do so, that he wasn't a POA or anything, was just helping grandma and she was helping him. That he was taken out of the house and away from the parents that then took grandma over will be in his favor. He won't be expected to understand a whole lot here.

If we were talking a granny with millions and he spent it all on him and the state can prove that, then maybe there would be a case against him. Currently there is none as he didn't keep records so what expenditures he made are unknown to him AND TO THE STATE.

I doubt he has much to worry about.
There is NO SENSE to having an attorney when he doesn't need one and it suggests "guilt". He should get rid of his attorney and wait and see. I think he has little to worry about here, but not knowing the details, who can really know.
This falls under wait and see.
The state is very busy. They don't waste money on invesigators on this stuff. They have guardianship given the by the court and have appointed a fiduciary to manage grandmother's placement and funds. This fiduciary isn't going to be investigating the grandson in my humble opinion.

Have the grand son get a social worker . He really has Nothing to worry about as Long as he is honest and tells His side of the story . There is nothing anyone can really do to Him. He took care of his grandmother . I have found Most APS workers to be Understanding they have seen it all .

Thank you all for your responses. Here’s a little more information to help respond to you all.

Unfortunately, due to her needing round the clock attention, he was unable to work as he was also working on his bachelor’s degree. He has no record himself and has never been to court, except when attending his parents multiple sentencing hearings. I don’t have much information about the attorney/their conversation because they’ve only talked once and are just waiting for the detectives to contact. As for neighbors, they all pretty much stay to themselves so I’m not sure anyone really ever paid attention, especially considering the house had pretty much turned into a drug house with random people in and out for a few months and no one said anything. Right now his biggest concern is the state is building a case against him and he’s going to go to jail because they will only look at the total amount spent rather than where the money actually went. I keep trying to remind him that the money was used for his rent/school (previously been agreed upon verbally and unfortunately not written). Then his GM/Dad’s property tax, bills, two car payments and insurance fees after dad totaled both cars. This also does not include the amount of money his dad stole/prevented from even being deposited into the account through forged SS checks. There were a few times where people showed up to turn off the gas/electricity and the only reason it stayed on was because he used the money to pay the bills. He would also take cash out to give to his dad because he was under the impression his dad was buying groceries for the house and other needs. He thought giving cash to his dad rather than access to the account was the smarter idea. He is just so nervous because there were times he spent money on some wants rather than needs. He truly had no intention of “depriving” her as the financial exploitation law states. I do apologize for the rambling in this reply. Just feeling helpless as it’s truly a waiting game at this point.

As long as he did not spend money after APS took over then hopefully he will be OK. If the money was withdrawn in small amts, it may not even be considered.
They are probably looking for large amounts of money thats been withdrawn. And Dad forging a SS check*and spending the money on himself, may mean jail time.

Since he was on her acct and given access to the acct, there should be no problem.

*I had to look it up. Most people now are direct deposit with Social Security. When my DH and I signed up back in early 2000s we had to take direct deposit. Seems over 500,000 people still get paper checks.

Perhaps an affidavit from someone in their lives who witnessed him caring for his GM would be helpful? A neighbor who knew he bought groceries, mowed the lawn, took her to the doctor etc. That he lived with her and kept regular hours and didn’t bring people into her home. Hopefully he is gainfully employed and doesn’t have a record of his own? It’s little more than a simple document that the neighbor or voucher would sign in front of a notary. That should be a stark contrast to what has happened to her with her son.
The bank will be able to show withdrawals and checks, who signed and what it was for. Large amounts of cash may have to be explained.
I am glad GS got help for his GM and she is being cared for.

Are most/all the funds in the joint account from her income sources alone? Did he deposit any of his own funds ever? It's possible the worst that may happen is that the conservator demands he reimburse those funds. Does his attorney have any experience with this type of situation? What does the lawyer say other similar cases have resulted in?

Advice on what to do? He lawyered up. That's as much as he can do until something else actually happens.

He needs to just tell the truth. It should be clearly evident from the forged documents and his parents' history that they are the abusers, not the grandson.