Ok so the only one left is in the Subrailnet (saving the man),then going to Obsidia poke center.
Or,saving the boy from the drifloon (I think its on the rainy day infront of the power plant gym),then saving him again from the venipedes at the Jasper Ward(near the poke center).His house is in Lapis Ward (which you will need to visit after the drifloon and before the venipedes,after that his at his house).
4sticker=5floor which seems is the max for ep11