@Beastwolf: Doesn't seem too difficult. The girls' roles as TF2 classes can be explained as a job they had, and this familial backstory can be placed before that.
I am interested, how you are going to retroactively add history to characters you break the 4th wall with and we already know the full origins of.
Do you have the skill?
Had to quickly google or TF2 Spy has any known brothers or sisters but I couldn't find it. Would be a surprising reference considering Anne is based on TF2 Spy.