Although I am a teacher, I grew up among farms (right next to the family farm and in the barn half the time). Cats were respected working members of the operation. The animals were usually tended by my mom, gram or me. (We didn't go to the doctor either unless it was life threatening.) So please be careful not to lump farmers and country people into one catagory...

Your father-in-law is a jerk. It is possible he says this stuff to get a reaction...something emotionally sadistic people often do... and would not actually do it. I had an uncle who used to say stuff like that. I used to remind him I knew way more about herbs than he did and if any of my animal friends went missing I might just make him something special... (I probably wouldn't have used anything lethal, but he wasn't sure and it did stop the comments.) Now my other uncles used to bring me orphaned bunnies (cutting hay is inevitably a problem) to raise and set free in the swamp where no one hunted.

I hope you get to move soon. Living in stress is awful.