First of all, who wears ear hairbands on christmas!? maybe reindeer horns hairbands but that's it.
Second, kinda hard to tell, there is no hint of hairbain in their heads, and, if i recall correctly, there isn't any form of ear hairband that looks like it lacks the "hairband" holding it. The hands could just be Anon wanting to grab Suika's ears or something.
Maybe TL would help to tell us if those are hairbands or not?
You lack of manga knowledge. First question, japanese people. Well Christian might not understandable. Second question, There is a lot of artist who don't draw hairband holder when draw hairband. Because not drawing give image more fantasy feeling.
All the mangas and animes i had seen while taking part in christmas, taking aside if one of the characters wasn't a catgirl/bunnygirl, they never put "cat/bunny ears" as part of the "christmas disguises", in fact they would either go with santa's hat or reindeer horns.