I would do this, it may not be correct but in a MH you have to think out of the box.
You did not say how old the kids are, if they are the age for front facing seats of either type. I would find your coaches seat belts and just use them. They are truly "seat belts" and will help. If the kids are in the rear facing seat age group, I guess I would use the seat belt and just strap them in, using their seat.
There is not really system for seat belt use other than the front folks. I would make sure you have an adult who can supervise the kids as they are going to want to look around and stuff while you are driving.
Good Luck safe travels