Answer:
"A design brief is a document for a design project developed by a person or team in consultation with the client/customer." They outline the deliverables and scope of the project including any products or works, timing and budget. "
It’d be helpful to add an image of the piece you’re asking about. This also sounds like something that requires a more personal answer, but if you post an image, I might be able to help you.
Answer:
This goes back to the Anglican Cathedral tradition of aniphonal singing. There are two sides to the Quire (the physical place) in a Cathedral: Decani (the side of the Dean) and Cantoris (the side of the Cantor). Thus, singing from side to side antiphonally makes sense liturgically.
Hope this helps!