Considering Vaas has slept with Citra, I don't think so.
Isnt Citra Vaas's sister? I think your mistaken or i'm not remembering this.
they both use the term brother and sister i think. dont remember anything about them sleeping together though. but, brother/sister could be being used in the same way as saying someone from your religion/church is your brother/sister. family is also used the same way quite often.