Information subject to change
https://elderscrollsonline.wiki.fextralife.com/Companion+Skillshttps://elderscrollsonline.wiki.fextralife.com/Companion+Equipment
Bastian: Resto Staff, 5 Light, and 2 Heavy. Mystic Fortress, Drake's Blood, Basalt Barrier, Searing Weapons, and Haste. Focusing on Quickened and Augmented to keep the buffs rolling and extend the duration.
Mirri: Bow, 7 Medium. Twilight Mantle, Piercing Arrow, Viper's Bite, Sniping Silver, and Vanish. Single target glass cannon, Aggressive and Shattering focused, do as much upfront damage as possible before she bites the dust.