Thanks @turquoisecoast yes we had offered to pay for them instead of gifts (we normally do KK but it always seems like a waste of $, we don't need gifts, would rather just the company on the day). Perhaps it is that they are too proud to accept us paying for them. I can't think of any other reason why they would refuse.
I'm going to invite them based on us paying but give them the option to decline if they'd really rather not celebrate. Then it's their decision they can live with. As much as it pains me I reckon they would be much happier playing golf on Christmas Day. Whatever, their choice. Knowing then I'll get a phone call 3 days before asking if there are still seats available 😫
I'm taking a back seat and just going to try stay out of it. It's hard when you love and care about them but they do have to make their own decisions. As long as they are honest with us - not going to get involved.