Comment by ydnaclementine

I've started recently, for an adult absolute beginner I would recommend: Alfred's Basic Adult All-In-One Piano Course (covers all types of music). A popular alternative is the Faber Adult Piano Adventures (more classical). Both books will go over how to position your wrists and fingers, music theory, as well as pieces.

I'm sure Alfred and Faber have books for kids. Check reddit and amazon. But you won't go wrong with books from either probably.

To accompany the books, there are videos where people go over the pieces from the books as a piano teacher. I recommend this guy: https://www.youtube.com/watch?v=e4gizue_ULg&list=PL8hZtgRyL9..., but just search the book name + piece name

Lastly since you're both learning, look into duet books and utilize the split mode on your piano