At the very least, they can be held items. Red Chu Chus hold red chu jelly, etc.
Except there may be no distinction between colors as they'd be the shiny versions, potentially. Not sure about this yet.
EDIT: On second thought, here's how I'll do it. I'll need a total of 9 creatures to be taken up by this.
From weakest to strongest:
Green ChuChu Family: Holds Max Ether
Red ChuChu Family: Holds Max Potion
Yellow ChuChu Family(Rare): Holds Max Revive
Of course the names will be changed, but I'm not going to call it Chu Jelly because I'm reserving that as one of the monster names. Think more along the lines of in Majoras Mask where these guys
Have hearts or magic bottles in them.
As a side note, I tweaked these guys to be smaller and look more true to their 3D counterparts:
And I've begun work on these:
I'm also adding this to the first post. It's a list of all the items in FRLG but with notes on whether or not it'll be used and what the new names will be. (?) means I don't know yet, and (-------) means I'm leaving it out of the game.
NOTE: I explained above why I think the pokeball crystals need to be changed to orbs.
And another thing to note... I think when it comes to overoworld revamping, in the GBC games everyone has 2 frames, and most people don't move. Only a select few do. I think maybe to stay more true to that style and only fully animate a few characters.(ones that would require walking)
.....and then there's this.