homeowners insurance problems

Can my children the steps to sue my father, a homeowners insurance dog bite your child has? My wife has custody.?
My son step lives here, was bit by our dog, the dog was presented and all expenses have been paid. No long-term problems with my stepson. As for me, and wife care concerns already taken, but his father does not live with him and not non-custodial parent is trying to sue the homeowners policy.
It is free, and anybody can sue anybody, but I think any reasonable judge / jury to see this money as a "for nothing" opportunity. If no no damage was done to the father, then what grounds does he have to sue?