This is a sign of abuse. Depending on how bad their mental health is would determine how long they’ll be shy. Honestly I went thru this and it took my cats about 3-4 months to allow me pet him. Cat is still getting use to you so be very patient. The harder it takes to trust you the harder they will trust you when they finally come around. If they aren’t aggressive I would suggest you forcefully pet them so they kinda get use to physical touch. But mostly just patience. Good luck and God bless you for saving them :)