Need Best Way To Protect From Deed My Dad May Have Been Tricked Into Signing (GA)

Three years ago my 94-year-old Dad was taken to a local law office and signed documents without me (only child). On the surface, it was a Probate action that removed my mother from the Deed to their primary residence since 1964. We are now concerned that the unrelated woman might have tricked him into also signing a deed, giving her ownership of the home after his death. His Will (in writing) is that all of his possessions are left to me. I've been told that if I'm now added to the Deed with my Dad (JTWROS) and 1) he was the original owner of the property (with my Mom), 2) I contributed nothing to the purchase and 3) he retains an interest in the property at the time of his death, I will be eligible for the full step-up tax basis after his death, not 50%, since it's being done for Estate Planning purposes. And this would also mean I would fully own the property at the time of death, regardless of any possible Deed he may have been tricked into signing. Does that sound right?