Richard
I can only agree with what others have said, I would add one other thing try not to anticipate anything and stay away from internet searches. They are very generic and often cause so much unnecessary fear.
Your Dad might appreciate some company and support at his referral and that might mean asking your Mum to go with him. It is always really helpful to have someone to make some notes and jot down any questions that come to mind. Your Dad might forget or simply just not take in all the information at the first referral or subsequent visits for tests etc.
You sound like you are very close to your Dad so he may want to involve you as well but of course that has to be his decision, if you talk to him and maybe your Mum too about what has been said here, or share with them the availability of the tool kit etc. Then that is a way to show you care and want to be involved.
The next month or so is going to be quite a challenge for you, so as others have already said try to be patient and appear calm as that will be a great way of supporting youd Dad and Mum.
Best wishes
xx
Mo