As queen of the anticipators, I had to learn to let go and live in the day by day. I realize you are a caretaker and I was a patient.
But some of what you fear may not materialize.

I think it sounds like he is doing fairly well actually. Keep eating solid food, supplementing with Boost, etc (Carnation has more calories) as long as possible. Keep up with the fluids. Have all the pertinent phone numbers handy in case.

I took my treatment away from home, and my husband had a job to work, so I had two sister-in-laws and a friend alternate time with me. They always encouraged me to take walks (walked with me actually). I took advantage of the classes held at the cancer treatment center, like yoga, (I was bad at it as it was 30 years since I had done any), meditation (both sacred and secular), and a combination of laughter & yoga. These things kept me somewhat occupied.

I know you have to get the supplies and food, so you have more to think about. I hope you can take some time for yourself to have something outside of being a caretaker. It is hard, but hang in there. It was hard for me to think about chemo, too. Your oncologist should have given you things to watch for, etc, when to call & so on. I was on the six chemo protocol instead of the three, so each of my six were shorter. Nevertheless they did not agree with me at all. I learned to take something for constipation before we started chemo, which helped for that side effect.

I'm sorry I don't have a magic solution for you. I wish I(we) did.
Best,
Anne