Legal Question in Real Estate Law in California

Your question does not make sense. You don't sign a grant deed for a loan.

Also, it is the family member you should sue; unless the lender had or should have had knowledge that it was a forgery, they would probably have no liability. After all, what did they do wrong?

The security device used to secure a loan in California is predominantly the deed of trust. A lender requires the person who holds record title or who is acquiring record title (usually in a purchase situation, using an escrow) to sign the deed of trust. If someone forged a deed to themselves, you will need to quiet title, and include the lender as a defendant when you quiet title.

I suggest speaking to a competent real estate attorney as soon as possible.