I say "Charlie" performs desptie having no nominations, a la "Finding Neverland". My guess is they do "It Must Be Believed to Be Seen" or "The View from Here" to show off Borle, who is technically a 2017 Tony nominee.
I would say "Pure Imagination", but showing off the chocolate room set is NOT going to do them any favors. Like, at all.
"Come From Away" should NOT do "Screeh In"; it's the most upbeat number in the show and gives the wron overall vibe. They should do "Welcome to the Rock", but I see "Me and the Sky" as an option since Colella is their acting nominee. But it's an ensembe show, so I firmly believe they should showcase the ensemble.
"Dear Evan Hansen" is probably going for "You Will Be Found"...but with Faist nomintated... "Sincerly, Me" may now be a contender (Though that would be like CFA doing "Screech"...it's a totally different number from the rest of the show).
If "Anastasia" decides to perform despite only 2 noms, I say go with "Once Upon a December". It's from the movie, and it will show off those beautiful, nominated costumes.
"Natasha...1812" should do the Prologue into "Dust and Ashes". Only way to get everyone in there and let it make any sense.