Dad has been diagnosed with colon cancer

Hi everyone, I'm not sure if I'm posting in the right area so please forgive me! I'm just here looking for a friendly chat and some help/advice on how to support my dad.

My dad is almost 65 and has recently been diagnosed with colon cancer. His cancer consultant has told him that it's been caught early and has not yet spread to other organs, although he can't be sure yet if its spread to nearby lymph nodes. 

Due to his age, he's been scheduled in for surgery to remove the growth quite quickly, 22nd June. He has to go in on the 21st of June so he can be prepared for surgery the next day. 

Understandably he's very worried. Just three years ago we lost my grandfather to cancer. He was 86 years of age when he died. When he was 78 he had surgery to remove a growth in his colon, however the growth was so big that the entire colon was removed and he ended up with a stoma. Fast forward a few years and my grandfather was back to his old self. He adapted to life extremely well with his colostomy bag and he never let it get in the way of anything he wanted to do. 

In August 2019, my grandfather called me one evening and asked if I could take him to hospital as he was struggling to pass water and was in a lot of pain. He never came home from hospital that time. His cancer had returned and spread to his liver and lungs, although we didn't find this out until 11 days before he died. He refused to tell the family because he didn't want to upset us. At first I was angry that he didn't tell us but he was such a strong minded individual, I understood why. When we eventually got told by his consultant, my world caved in. I was very close to my grandad, he'd helped me through a particularly bad time in my life where I suffered extreme anxiety and depression, and we were told he had just weeks to live. 

I was at his bedside for hours each day and never once did I hear him mentioning how much pain he was in. I admire him so much for tackling his cancer head on. He knew he wasn't going to beat it this time but he gave one hell of a fight. He knew he didn't have much time left but he always had a smile on his face. 

Once he passed, I had 4 months of grief counselling and even now I still can't believe my lovely grandad isn't here anymore. I'm 33 years old and now I'm extremely worried about my dad. My dad isn't dealing with his illness very well and I don't know how to help him. His wife, my step mother, has been amazing but he is struggling mentally. 

I realise this is a long post but does anyone have any advice on how best I can support my dad in such a worrying time? 

Thanks in advance x