If you look at the center of your bus and see the seat bolts in the floor you will see where they should be underneath. They almost all have nuts, except the few that go into areas not accessible from underneath. some may go through floor ribs and have longer bolts.
Steps for removing them:
If one person, try an impact driver and socket in forward and hope they are rusted enough to snap them off at the head. If not lucky, like me, they will spin in their holes. In that case someone under the bus and someone up top with sockets.
Some will just need to be cut or ground off.
If you're not seeing nuts, it's because they are buried in road grime.