well, at this point they haven't since Sherry/Jake is still in Eastern Europe (they met Chris/Piers during six months before) while Leon/Helena is in Tall Oaks. Leon/Helena won't even go to Eastern Europe, they only going to China. so yeah, Sherry/Jake will meet them during the plane crash site where the crossover event occur fighting with Ustanak.They might as well as have met Leon at this point since she mentions him and Claire but Jake isnt even asking about him, only about Claire. Also at this point they have met Chris since Jake refers to him talking about Claire "Claire is that BSSA guy's siter, right?"
well, at least that's what i think based on the stage level that they revealed.