Your barge stays on Florida time, while Cozumel time varies - and in May I think it will be on Central Daylight Time. 1pm on your boat will be noon on the island, if I am not mistaken - so that would help. Two other things would help...
Charter a private boat perhaps. For 5, it should be the same cost as 5 going with others.
Carry a cane every time you board & leave the barge so they will put your group in the fast lines.

It worked for my daughter's group last week after she reinjured a knee and showed up in a brace.
But you have 11 months. Maybe you can get the two other kids certified before then?