Is forcing a sick father to undergo surgery without his knowledge—out of a desire for his recovery—considered disobedience to him? And what if the father dies because of this surgery; would the son be considered to have caused his death?

There is no blame upon you in that, as long as you intend good and benefit for the the patient and do not wish him harm. You are a doer of good, and it is hoped that you will be rewarded. Even if the patient dies as a result of the surgery, there is no blame upon you if the surgery proceeded normally and there was no negligence, and the doctor was qualified, and the conditions were met; for Allah says: "There is no way [of blame] upon the doers of good."