Hey there, Tania!
Thanks for bringing your great question to the Disney Parks Moms Panel. I think it's just wonderful that you and your daughters want to match to show your holiday spirit during your visit to the Happiest Place on Earth.
It sounds like you are interested in wearing some "onesie" pajama outfits to the parks (which sound very comfy I must say). While these outfits are not explicitly costumes, its possible they could be perceived as costumes
which are not allowed to be worn by Guests 14 years or older inside Disneyland Park or Disney California Adventure Park. Ultimately it will be up to the discretion of the Cast Member at the park entrances if they deem this attire appropriate. If you want to wear them, I would say to be prepared with a back-up outfit in case they are not permitted. I'm sorry I don't have a more definite answer for you.
Another fun way to show your Disney Side and holiday pride would be by
DisneyBounding. This involves wearing everyday clothes with the iconic color schemes and accessories to channel your favorite Characters. You could wear a reindeer headband with a brown shirt, skirt, and a red bow necklace to still pull off a cute reindeer look without worrying about breaking any park rules. This is such a fun way to show your creative side as well.
I hope this helps, and have a magical day!
-Jennifer