This is a lot of fiss about nothing. "Disabled" means many things, but I presume that OP is referring to an individual with a disability requiring time and assistance. If so, the individual and perhaps one person to help.

The other three would be next in line to board as First boards, well, first. Either way, those people board as #3 , 4, and 5.

This is a problem only in "lesser classes" where it seems that some believe that one person who requires time and might well prefer not to have a hoard, becomes the bonanza for a group of well-abled passengers simply not willing to wait their turn.