Mine have separate ones, as different colours, although I use some items (plastic and rubber curry combs) on all as I have every day items then 'best' brushes that never get used lol!! It's just easier to use the same items on them rather than go back and forth to the tack room to get their own brushes, how lazy is that lol! Also little pony has another child size grooming kit for the kids to use on him. Oh and when I got my new horse I had a nearly new grooming kit that was for a pony we had on loan that became my new horses kit. save buying a new one when that was ok.
They have their own headcollars, but I quite often use the same one on them again to save me going to the tack room to pick up their own ones.
Oh must add, at the moment I am using separate brushes on my old man due to his skin condition on his back legs, don't want the other two getting anything just incase they could.