Below are the answers:
11. Polytheism was probably an extension of animism, which shows up in a lot of native African religions. As for monotheism, well many slave-sellers were Muslims and many slave-buyers were Christians.
12. Art was used to celebrate African religious beliefs ,told stories ,and served.
13. By letting them know that family is also a part of a larger segment of more distant cousins and their families, who will stand with each other when attacked by outsiders.