I'm going to watch ALL Star Wars movies this Christmas.
In what order should I watch them?
I would suggest that you don't. Not all "Star Wars" movies are
Star Wars movies, IMHO.
The sequel trilogy made under Kathleen Kennedy/Disney
retcons a bunch from the old movies in destructive ways that are quite disagreeable with a lot of people. It was not conceived according to a long-term plan. Episode 8 got a rogue director/script writer that probably secretly hated Star Wars, and the result is a mess. The follow-up episode 9 is a really bad movie (from a movie-making perspective) - a patchwork trying to make something cohesive out of the mess from episode 8, and it still changes the lore in destructive ways from the older movies. Avoid that cringe and save your energy and sanity!
You could also skip Episode 1, to avoid some cringe.
A popular watching order is the "Machete Order", but you could add Rogue One which ends precisely before Episode IV - A New Hope begins:
Rogue One
Episode IV - A New Hope
Episode V - Empire Strikes Back
Episode II - Attack of the Clones
Episode III - Revenge of the Sith
Episode VI - Return of the Jedi.
The Mandalorian seasons 1 and 2 (episodes 1..8 and 9..16)
The Mandalorian season 2 (episode 11 and on) have some references to the computer-animated TV series The Clone Wars and Rebels, but those are not necessary.
The series are also canon ("gospel"), but they are made more or less for kids so they are tonally different and of varying quality (and cringe). It would also take a long time to watch them all, and there are also quite a few "filler episodes".
The Clone Wars is set between Episode II and III, except for the last four episodes of season 7 which overlaps episode III. Rebels is set after Episode III chronologically.
BTW. The first seasons of The Clone Wars are also not in chronological order: there is an official chronology somewhere compiled by Leland Chee of Lucasfilm.