You can detach by letting go of concern about what the in laws are doing or thinking, and refocus on what does work in your life. You'll do fine. You can adjust and fine tune your decision as you go along, based on results of your experiment.

You don't even need to announce anything or make a huge change, you can just redirect your energy. This is a great time to renew healthy hobbies and interests.

I'm glad your husband understands.

I understand from experience the feeling of being immobilized. I think the answer is to do things you enjoy and love. Play, find something to laugh about, don't let the chill of the in laws freeze you anymore. Freezing you out, that is their loss. They are missing out. That is their choice, so you get to make your own choices, and focus on where warmth and health is.