What is likely to happen next?

Hi not enough information to be honest. Weight will be a problem it might be worth looking at power of attorney to be able to act on his behalf particularly if he is confused. But he may be trying to filter information he’s sharing with you being a parent doesn’t stop no matter how competent an adult we become and of course there is the ‘I don’t want to be a burden’ thing too. 
might be worth booking a call with his names nurse with your fathers consent to help you both understand what’s happening. 
also he should get a letter after his consultation that sets everything out clearly. 
I do hope you can find out what’s going on clearly so you can both move forward with a shared truth. 
take good care of you too it’s a lot! 

Hi,

Although I don’t know the details of your dad’s case 6mm seems smallish for a kidney cancer I think, my surgeon said they grow slowly below 4cm. Mine was 20cm and I had very few symptoms and no pain. Also the most common kidney cancers are slow growing, so they may adopt a watch and wait strategy. My cancer team were more than happy for my family to attend appointments with me as sometimes it can be hard to take all the info in. 
Next for me it was more detailed scans and then an op, I am now waiting for immunotherapy, I find that prognosis and treatment are changing as they gather more info. 
Best of luck to you and your Dad on this journey.