I'm sorry to hear about your dad.
If he can handle butter, adding that to cream soups will certainly up the calories and nourishment.
If you have access to healthful chickens, maybe make up a big batch of bone broth, but leave the meat on the bones (cut a whole chicken into at least eight pieces). The broth, once you've taken out the solids, can be simmered down for bases of other soups. If he can't handle all the fat from the chicken skin, take that off before you make the broth. The saved chicken can be used on the days he can handle a bit.
Creamed potato, squash, root (with cream cheese, cream, and/or butter) soups will provide calories. If he likes the pumkin soup, he might also like sweet potato soup.
Hugs to you and your family.