Signers on a Mentally Disabled Individual's Account

I have a situation where a person's care has been turned over to the county. He currently resides in an assisted living facility. He is mentally disabled and cannot sign his own name. His parents would like him to open a checking account to pay for daily items, bills, food, etc. The question is: 1) May the county, although not legal guardian, allow his assisted living home sign for his purchases and manage his account (since the home will be the ones with him when he makes his purchases), and 2) what is the best way to choose the signers for his account to verify that the funds in his account are "safe"? (preventing exemployees, or current ones for that matter, from taking advantage of their position of signing for him.)