1 Could you use the name of the place where you did the research? If they specify the third person for one part, I don't see why you have to use it in the other parts.
2 American tend to use the singular. British speakers tend to use the plural a lot more. I am not sure that there is a Commonwealth standard- I believe Australians use the singular more than we do in the UK. What's the position in Nigerian English? Also, plenty of British speakers do use the singular- it's more a question of usage than a rule to me.
In the case of Led Zeppelin, Jimmy Page uses the singular- he describes one live recording as Led Zeppelin 'at its best', while I would say 'their best'.