Aww that is a LOT on your plate.

Like Bookworm, my first suggestion was going to be replacing the kid that causes so much extra work and stress, but if you want to keep him, I guess instead of "removing stressors", you'll have to focus more on self-care, and doing more things or claiming more time (from somewhere! I know it might not sound easy) to take care of yourself and release some stress.

Is there anyone else that can help with her cat? I know it would suck with a cat in the house who is refusing to use the litter box. I can understand how your mother-in-law would be worried about her pet too though. Are there any other options? Did the cat just start with the litter box issues when she went into hospital, or does he/she have those issues when she's home too?

I hope things get a little brighter and more manageable in your world soon. Hugs to you.