Before modern medicine, in which treatment's with certain ethical therapies and medication, most patients with mental illness where placed in institutions no matter how severe, and were forced to go through unethical therapies such as electroshock or lobotomies.
Review the candidates work history
Prepare "KEY" interview questions
Review the job description. Thoroughly familiarize yourself with the job description especially it's hiring criteria
Let them know that you arent there for their satisfaction. Make sure that your voice is heard and do not let them take you for granted. The best thing to do if they are becoming too much for you is to leave them.
The best thing to do however is to just talk to them. Talk and see why they are acting the way that they are.
I really hope this helped hunny and I hope everything goes well!