Mobile-first design for many-to-many relationships

I am trying to figure out the best mobile-first design for many-to-many relationships. For example, a list in which the elements contain drop-downs with multiple-selection, e.g. check-boxed items? Let's say your data is Authors and Books. Each data type has numerous attributes that need to be editable. Drop-downs are not usually mobile-friendly, especially ones with check-boxes so I am looking for better alternatives.