The Adventurers League FAQ states:
Can My Familiar Attune to a Magic Item?
Any item attuned to an NPC under your control (such as, but not limited to, familiars, beast companions, simulacrums, conjured creatures, hirelings, lickspittles, etc.) counts against both your character’s limit of three attuned items and the character’s permanent magic item count.
This rule doesn’t imply that such creatures have the ability to attune to magic items. Whether or not a mindless undead creature—for example—can attune to something is subject to DM discretion.
If you have a simulacrum/familiar attuned to an item, are you also considered attuned to it, and therefore able to use it too?
My uncertainty comes from the fact that it states that it counts against your attunement slots, but not that you are considered as attuned to it (perhaps it's implicit, perhaps not, I'm not sure).
Ex: Bob the Wizard has a Simulacrum, Bobtwo. Bobtwo is attuned to a Staff of the Magi, and casts a Web spell with it, then hands it to Bob as an object interaction, then Bob would, on his turn, cast an Invisibility spell with the same Staff.