That is just ridiculous. It's possible to switch them over, but it will probably take awhile. However, some snakes will actually starve themselves to the point of losing weight and becoming unhealthy, especially if they are used to eating live. I would recommend looking for either your own place or a possible new home for your snakes.

I don't want this to come across in a mean way, and I understand you're in a difficult situation, but these 'rules' that you have to follow regarding your snakes care run the gambit from stressful to actively harmful. You can't mist and are apparently made to give them pre-shed soaks, I don't know if it's been resolved but you weren't allowed to provide adequately sized/enough feeders, you aren't allowed to properly gauge temp and humidity: These are all things we would insist new keepers have/be able to do before they went out and even purchased a snake in order to provide for its basic needs. If you can't provide these things, the proper thing to do is rehome the animals.

That being said, I hope you can get him to take f/t. Will your MIL consider allowing pre-killed? That's often an easier stepping stone than going straight from live to f/t.