Two weeks will make a good dent, and be invaluable for your father during his immediate recovery. You say your sister lives nearby, so if she could check in on him in the evenings, maybe? Take the offers of help that you've received (whether or not she can cook!) because it might well be needed. See if there's any possibility of a visiting nurse who can come in daily for a while...
Many people have fussy appetites after surgery, it can last a while. Fatigue is a serious problem the first month or two as well.
Yes, there will be foods that contribute to healing or distress, I'm pretty sure everyone receives information before leaving the hospital on what to avoid (dairy is one thing, I think). Getting the bowels back to work is the main issue and it can take a good month before things start getting back to 'normal'.
The uro and his assistants should be able to answer your questions about how much help will be needed as well as how to go about pursuing the best diet possible post-op. You'll need to take it all one day at a time.
Your father is lucky to have you.
Wendy