Hi Candy
I have no experience with the surgery so cannot comment. However, I have a suggestion for finding out what you need to know without freaking your Dad out.

People have different reactions to illness and some just want to get through it and don't want to know too much in advance. Others want to know all the ins and outs of everything so they can prepare themselves. Doctors are used to this and it may be worth requesting either that the first half of the appointment is with your dad and the second half is with you and your Mum (if she wants to know more) or that you have an appointment of your own to discuss your role. Also, these doctors are happy to answer questions by email or put you onto someone who will.

Do you have a co-ordinator? We had a nurse who looked after a lot of our issues and answered all my questions outside the hearing of Alex who didn't want to know anything.

I believe that the carer(s) have equal rights to know about prognosis, treatment and future management as well as possible complications, likely issues but they do not have the right to force this information on the patient if they don't want to know. You clearly already know this as you have already reacted to your Dad's apprehension by not asking the questions you need to know the answers to. I wish I had had your sensitivity and wisdom at the beginning (I am getting better at it now though :)).