When I leave my tank in someone else's care, I do the following:
Full containers (jugs) of top up water beside the tank for ease.
Salt water mixed and ready in the event of an emergency.
All maintenance completed (skimmer emptied), double check all equipment is functioning correctly (heaters, ph) etc. Water change a day or two before leaving
Food prepared as noted earlier
Any special instructions are written and left within view of the tank. I actually leave full instructions regardless.
Label equipment and cords so if something does happen, they know what's what.
If going somewhere where I am not available, I've asked for another reefer here if they could be available to help if anything was to come up.
Not sure what your temps are like, but we are warm, so I'd make sure he keeps an eye on the tank temp depending on what you have for equipment to keep it cool.
Otherwise, go enjoy your visit with your mom!!
Your tank should be fine for 5 days!!!