Do any other Overwatch heroes know Soldier:76's and Reaper's real identities?

In the line by Pharah, I don't think she's implying that S76 doesn't know Ana. I think she does know he's Jack and she's implying that, while he has a working relationship with Ana, he doesn't know how she is as a mother or the relationship between Pharah and Ana.

To answer your question, Mercy seems to be aware of Reaper's identity, as demonstrated in this voice clip:

Winston also has some interaction with S76 that suggests he knows but I can't find the quote online, I'll look it up and edit this post if I find it.

Also it seems Reaper and S76 are aware of each others identity.