What liabilities/responsibilities will I incur if I become a co-executor of a trust for a family member?

My mom is setting up a trust for my uncle whose disabilities prevent him from exercising reasonable independence in financial matters. She asked if I would be interested in being a co-executor with her of the trust in the event she is not available to administer it.

I’m more than happy to help, but I also want to know what legal tethers I’d be signing up for.