Stressed cat weeing everywhere?

You stated that your baby has been to the vet twice in the past week, did they check for uti(urinary tract infection)? It is probably stress and I, too have heard really good things about the "Feliway" diffuser, but sometimes a uti can cuse the same symptoms. Also, love isn't enough it may actually take some serious quiet bonding time with this kitty by his temporary adoptive family to calm him enough to change his behavior. What I mean is sitting and holding and petting him for up to 20 minutes several times a day (good time is in the evening in front of the TV. Hope this helps. Good luck and God Bless.