Expand your Population , HOW ?

First , you need Community Buildings to increase your Population Cap.
Second , you need neighbours to be a part of the crew for your building , UNLESS you wanna spend City Cash (which you probably don't want) . Some of your neighbours wouldn't know that you need a crew for your building so you have to ask them nicely to be a crew member of that certain community building .
Third , you need to build houses for your people .