My mother and her three children have held joint bank accounts for over 5 years. How is this viewed when applying for Medicaid?

Unless there was no activity at all after initial combining of assets, it's a possible mess.  If you have instead activity where money was deposited by persons in addition to your mother and spent by persons other than your mother, Medicaid could view all monies in the account as Mom's. if so, you will need to have a breakdown of who contributed what, who spent what for whom, and it will be a real mess if you have lots of cash transactions. If there is enough money involved, an elder attorney would be advised. If the only change was to add persons as TOD transfer on death and no one else put money in or out, the attorney can help you explain. If money left account within five years of application date for Medicaid, be prepared to explain if not directly related to parent care. If money for caregiving, better have a contract and tax records. Good luck.