Incremetal load from 1 fact to another fact

Hi
i have a situation.

There is a fact A and fact B which acts as a source for another fact C. The Fact A and B contains detail values which are loaded daily and Fact C contains aggregated values which is loaded weekly. Fact A and B contains Source_file_name, source_file_date information in them but fact C has no file informations. My questions are

Is it a good practice to have multiple facts as source for another fact?
If yes, then how the data sould be loaded incrementally in fact C?

Regards
Vibhuti

'Is it a good practice to have multiple facts as source for another fact?'

Of course... that is what an aggregate fact table is.

'If yes, then how the data sould be loaded incrementally in fact C?'

There are a lot of ways of doing it. It all depends on what the base feeds look like and how you are updating the base facts. But the simplest is to pull last week's facts from the two tables, aggregate them and push them into the target table.