Have grandparents apply, and be on lease? Or just the parents?

[Kimberly T.]

We have a couple who is interested in our rental house. They have 3 kids. Both parents have some upcoming work obligations that will require them to be away from home for an extended period of time, so what they want to do is have the wife's parents stay in our rental house for a while to take care of their kids (get the kids to school, go to dr appointments, etc.). The couple will be responsible for paying all the rent. The wife's parents will not be contributing to the rent, but will probably live there around 9 months.

We will be having the couple apply for the rental through Cozy, but we're not sure if we should have the wife's parents also apply, and/or whether we should put them on the lease? What do you all think?