QI summon this follower with Sahaquiel's Fanfare, giving it “At the start of your end phase, return this card to its owner’s hand.” Do both "At the start of your end phase" abilities trigger?

AYes, and you may choose the order in which they resolve. Note that even if you choose to return this follower to your hand first, you would still give each other follower on your field {ATK}+1, as the ability is already pending by the time this follower has left the field.