What a sad but heartwarming story about your Sandi. If he knew love and was a lap cat before, I'm sure he will gradually be that way again.
The other woman who adopted him first obviously has no knowledge of cats. Stupid move on her part for sure.

Just sit in the room, on the floor, humming quietly while reading a book and you'll be surprised of the outcome. I had to do this with a very scared stray, many years ago, and he gradually came around on the 4th day of doing this. Each day after that he became more and more secure in me and his surroundings.

Prayers on the way that everything will work out for you and for Sandi.
He needs you as much as you need him.