If an animal is scared, it can trigger a seizure too. I took a stray kitten and her family in one stormy cold night and put them in a different room than my cats. They were in a storage room but I figured it was better than being out in the cold for the night. Well, a bad thunderstorm moved in that night. All the cats were fine except one. When I took them back outside the next morning, she went into a seizure. I called the vet and was told all the changes and frights she had could have triggered it. She recovered and never had another so we were fairly sure it was because she was so scared. What I'm trying to say, is if Presley is scared of his former owners it would be better if you could keep him from them entirely. Maybe put him in a room they won't be in and give him some extra toys or treats while they are there. If they say anything just tell them it's vet's orders while you are trying to diagnose him.