Heh, Steph and Roy HAVE met. Once. And Steph and Connor have met on multiple occasions. Cass has met Connor as well. She knocked him out first time they met. >>;;

Steph+Roy met: Teen Titans v2 #17 (only meeting and Tim was there too)
Steph+Connor met: Robin #25 (which went to Robin #26)
Cass+Connor met: Batgirl v1 #30 (then Tim & Steph join them in Batgirl v1 #31-32)
Steph+Cissie: Steph was part of YJ for some of the final fights, in that big crowd? They could have talked? (EDIT: Nevermind, that was Bonnie pretending to be Cissie. Ah well.)