Would you invite this person over for Christmas?

Why in the world would your parents have the gall to think a GUEST in their home "should help"? That is the height of rudeness. He is a guest in your home and shouldn't have to "help" with anything so they have zero right to get "annoyed". If anything I would tell them to take a leap if they invited me over and then had the nerve to expect me to help with something and wouldn't want to go over there. Your folks need to learn how to be good hosts and not expect guests to help out with anything.

Add: If anything YOU should help them and as someone said, you need to leave this for the grown ups and not try to get people to side with your mommy and daddy against a guest in their home. Good hosts don't expect guests to pitch in and help out. That is YOUR job as you do live there. Clearly your parents don't have very good manners and are teaching you bad manners as well.

I would invite anybody that’s not violent a sex criminal or a bully like my sister.  

I think, Dylan, that if your parents wanted your input and judgment they would ask for it.  As fascinating as this is, what I would do is immaterial.

Fortunately, Dylan, you're in a position where you don't really have to do anything, since this is really just between the adults.  You're in the "rocking chair" for this one.

But it's good that you're thinking about dilemmas like this because you'll be an adult soon, so you might as well start practicing the process of reasoning it out.  Just don't complicate the adults' lives by tossing in your two cents' worth.  Keep your opinion to yourself - and watch what they do and how it works out.  It'll be an educational experience for you.

It seems like your folks are being guided by what's good for THEM - not necessarily what's good for your uncle.  Basically, Mom & Dad want to avoid feeling guilty.  That's understandable.  They think dragging your uncle through a family-centered social event is something that benefits him and they don't want to think of themselves as having denied a family member some teensy bit of annual benefit.  Perhaps your uncle has some special needs, and they wouldn't want to think of themselves as uncharitable.

Of course, the evidence leaves open the possibility that your uncle sees this as a duty, not a benefit.  After all, he chooses to have nothing to do with you the entire rest of the year, and when he's there he just sits in one place.  Ah, but nobody can be sure, because none of you really know each other and don't WANT to get to know each other.  The only way to find out what these Christmas dinners mean to him is to actually talk to him about it - and everyone can't imagine that being anything but traumatic.

People are funny that way.  They'd rather passively be the victims of a lot of inconvenience or unpleasantness than make a decision that's likely to involve...well...the very same inconvenience and unpleasantness.  Nobody wants to find out whether Uncle likes or loathes Christmas dinner with family, so you're very likely to just continue having family dinners with Uncle.  (And, it must be said, this is a two-way street.  It's possible Uncle doesn't want to have to say "I really would prefer to pass up the Christmas tradition" so he just keeps having to endure it.)

Here's an idea:  Why don't you and Uncle watch a Dickens "Christmas Carol" movie together, and then you ask him if he identifies more with the Pre-Ghost Ebenezer, seeing it all as a bother, or the Post-Ghost Ebenezer, all full of the Christmas spirit?  Perhaps that'll help you decide what you'd do if you were an adult, in this case.

Everyone should be wearing masks except while eating. Even that is risky.