Help- How can I get my grandparents to access bereavement support?

Hi everyone, I hope you can help? (Apologises for the long post, I felt some backstory was important).

Last December, we unfortunately lost my uncle R to cancer that he had been fighting for a couple years. Whilst I think we all knew he wasn't going to get better, his passing still broke us and as it was near Christmas, it made things 10x worse. After a few months had passed, my uncle P (his twin brother) was diagnosed with the exact same cancer on the day we had decided to scatter his brothers ashes. To make this worse, it turns out he'd had cancer for 10 years undiagnosed and growing by the year- you can imagine what this meant.

By some miracle, he's had the surgery to remove the cancer and seems to be doing really well, but the series of events between my two uncles has seriously affected my grandparents emotional wellbeing and mental health (especially my grandad). I don't want to sound awful, but I also feel that my uncle P being able to survive this has become a constant reminder of what my uncle R never got to have and that is really hard.

When we visit them, it is like speaking to completely different people who are emotionally shut off. They never want to engage with us or when they do, they aren't themselves (expected, but difficult to watch). They haven't reached out for any support but I really think they need to speak to someone about their emotions as it's hard for us as a family to move on together when they are suffering and won't access support.

Any advice would be greatly appreciated. I've been advised to try and call Macmillan with them, but I don't think they'd be up for discussing their grief in front of us.