RNA-seq: How to get new expression count after normalization
If I'm interested to get normalized gene counts, can I go ahead and
  multiple each individual's norm.factor into its gene counts? For
  example, the expected count for IND1 for Gene1 is 100 and it's
  norm.factor is 0.80, can I say that the normalized gene count is
  100*0.80=80?


No; you divide, but if you poke around, you can probably find a way to get edgeR to return the normalized counts.


  I think since normalization uses per person library size, each
  person's normalization is independent of the others.


Not true for the default normalization used in edgeR, TMM.  CPM normalization is independently determined for each sample.

In general, normalize everything together, unless you think that the algorithm assumptions might be violated by including all of them together.