Question on London consulate and dual applications with US documents

I have two questions I am trying to answer:

1. If there are two citizenship applications at the London consulate for siblings based on the same ancestor do you need to provide two copies of all documents relating to the ancestor or can a single set of documents support both applications?

2. If the ancestor has US documents relating to them (marriage, non naturalisation etc) can these be translated in the UK after being apostilled in the US or would they have to be translated by a US certified translator?

If anyone has any knowledge or experience of these questions it would be much appreciated.