Hi Mysonny,
First of all, you are a terrific caregiver. Believe me, they need your support right now.
I used to make all kinds of different soups for my dad - potato, spinach, carrot, eggplant, red beans, corn etc.(it was the only thing he could eat post surgery. Also, making sure he gets enough calories is really important. Stock up on protein cans - the flavored ones tastes good. Avocado juice with chocolate condensed milk is another thing that is good and high in calories.
Some research shows that soursop, wheatgrass, and aloe vera has helped in cancer treatment (building metabolism, immunity etc).

Good luck on your journey. Keep believing and have faith that everything is going to be okay!

Hugs