I'm writing a song and there is a line:
When they got heaven by their sides
I am not sure whether side or sides is correct in this context. Thanks!
This depends on what your intended meaning is.
If you mean to say "they" as in a group have heaven by their side, then you need to use side because you are talking about the entire group having heaven on their side.
If you mean each individual person has heaven by their sides, then you use sides because there is more than one person's side. Your intended meaning will affect this.