Colon cancer and troubles with eating, bowel movements and nausea

My dad is 90 yrs old and has been exceptionally independent and healthy until he was diagnosed with colon cancer 6 months ago. While his cancer was in a good place to operate once He had exploratory surgery they could not because they said the 2 tumors had attached themselves to the pancreas and duodenum . After this surgery he went downhill feeling extremely weak,little appetite and unable to sleep. He was hospitalized for bleeding and given a course of 5 radiation treatments to stop bleeding and hopefully stabilize him. After the radiation nausea,vomiting and diahrrea persisted for 2 weeks and he was unable to eat, and he lost over 30 lbs. throughout this time he was on zofran, an anti nausea medication for cancer patients after treatment, which did not help despite increase in dosage and being told that it was the best medication for nausea.he was again hospitalized where he started to eat a little again. Once home he was eating a little better and was on zofran 4x daily. He then developed constipation which cleared up but now still having difficulty eating , vomiting and afraid to eat because he worries that he will vomit. We try to encourage him to have little sips of foods/drinks he likes but he becomes agitated with us.
Has anyone had any experience with this issue with an elderly parent and what could be done to correct nausea and vomiting to help him eat. He also does not sleep which does not help with his mood(note that prior to all this he never had sleep problems)
Thanks for any feedback.