If my grandfather dies and still owes an excessive amount or credit card debt and loans can his house be seized because of this debt?

Ok, if your grandfather dies, and his wife is already passed away.

The property goes into his estate. His house, his car, his bank accounts all go into the estate.

It is not that the house is "seized" but whoever is over the estate, will take the money he has, and will have to sell the cars and the house, to pay the bills. After all the bills are paid what ever is left goes to the family.

As Chuck said, they can't "seize" the house, but they are entitled to be paid from the value of the estate. So basically any assets granddad has must first be used to repay outstanding debt. Only after his liabilities are paid, can his heirs get anything from the estate.

On the flip side, if the value of the estate is insufficient to repay all the debts, then the creditors are out of luck.