Can familiars use/attune to magic Items? Yes they are creatures and can use magic items.

Can animals use magic items 5e?

A D&D creature can use magic items, unless its anatomy or a rule precludes such use. ... Ultimately, the DM decides, guided by the magic item rules in the "Dungeon Master's Guide." #DnD.

Can mounts attune to magic items 5e?

Mounts and Attunement

The rules state that "a creature can be attuned to no more than three magic items at a time" and a mount is a creature. ... Any creature a mount trusts implicitly can attune a magic item for them.