David my three cats all live on dried cat food - and it's recommended by my vet., it's much better for the cats - they must have constant supply of water. I bet your Mom's catswill be good and healthy.
If they won't take to the dried food straight away try mixing tinned food with it. Then you can reduce the tinned food until their are are dried food only.

Goodf Luck - hope it all turns out OK.

Lynne