Opaque, a very unfortunate situation indeed. And in addition to having to worry about them and for the community as it goes for Covid, I assume you are also worried about what kind of a rabbit hole they have fallen or about to fall into? I at least am very worried about what sort of weirdness these people can cook up.
You are right that it's no use trying to argue them out of it. Apparently opposition views tend to only strengthen the convictions in many cases.
However, as long as this concerns adults (which I don't of course know), it really is up to them. You can't make anyone see sense. If it would be possible to keep the relations with them alive, for example to agree to not talk about this, it might be helpful, to hold on to a normal life to return to if some of them start coming around. However it's not your responsibility to "save" them from themselves, or from Q. You can offer a hand but they must take it, so to speak.
It's easy for me to say, but you are also under no obligation to go to the family gathering. While it may feel bad to do so, you are entirely within your rights to just say, thank you for the invitation but I'm not coming this year, and then inform the asker that you will cut the conversation if they pressure you to go or to state why you don't want to go. I'm sure you know this in theory. I also know it's much much less easy to do it in practice!
As it is, I can only wish you luck, and strength. I hope their treks into the rabbit hole will remain relatively shallow!
Finland is lifting restrictions, although the case numbers are getting worse again. A bit over 80 % of over 12 year olds have had the first vaccination, but the second dose is lagging at around 70 % rate and is slowing. We can't really keep everything closed forever, but now again everyone is suffering from the decisions of these who won't take the shot - intensive care units are getting busy, which means various treatments and operations that would likely require ICU as after treatment will soon start getting postponed again.
Finland has just banned giving the Moderna to men under 30 ya due to possible elevated risk of inflammation of the heart. This sort of thing of course doesn't really help to put the anti-vaxxers at ease. Also my son has had the Moderna but he's fine so far.
It's still a mess.