There are two questions here:
1. Can your grandfather be held accountable for your home loan, and
2. Can the plaintiff go after your grandfather's assets if he is responsible for the loan?
First, if your grandfather signed on the loan as either a borrower or a guarantor, then he could be held responsible for any default or shortfall. His credit rating will surely suffer a hit from the non-payment and if the foreclosure auction does not generate enough money to cover the loan, the plaintiff could pursue a deficiency judgment against him.
Second, if the plaintiff obtains a deficiency judgment, they could attempt to use his non-exempt assets to satisfy the debt. This would include some investments like stocks - except those held in retirement accounts - and real estate other than his homestead. (Some exceptions may apply.) If he dies, they may file a claim against his estate.
In order to prevent a deficiency judgment against your grandfather, and to protect his assets, you'll want to talk to a foreclose defense lawyer.
If you want to learn more about how a foreclosure defense can protect you and your grandfather, you can download our free 30-page ebook that talks about Florida foreclosure defense.