I hesitate to post because I don't want this to become a "more disabled than someone else" thread. I just want to gently remind people that not all disabilities are visable. And even if you can see the disability you don't know the extent. So just because someone is in that seat and you don't see a wheelchair, they may still be disabled.
I think there was a more indepth thread on this a bit ago, but I can't find it right now. Here is the language I find for use of the those seats.
"Sec. 38.27 Priority seating signs.
(a) Each vehicle shall contain sign(s) which indicate that seats in the front of the vehicle are priority seats for persons with disabilities, and that other passengers
should make such seats available to those who wish to use them. At least one set of forward-facing seats shall be so designated. (b) Each securement location shall have a sign designating it as such."
http://www.fta.dot.gov/civilrights/ada/civil_rights_3905.html
I don't think the bus driver is able to "kick them" out of those seats.
Perhaps Magicbus will stop by with some words of wisdom on the subject.