Renting an apartment in san Diego ?

we are a family of 3, when we moved into this apartment in san Diego, the rental manager said that for a 2 bedroom unit they only allow 3 people and for a single bedroom unit only 2 people is allowed. when we were at the office there were two other fAmilies that the manager turned down because she said that they have rules that maximum if 3 can only live in a two bedroom unit, but when we signed our lease there was nothing on the agreement that says we cant have more than 4 occupants in the unit,our dilemma is this we have been living in the apartment for more than a year and now we are expecting our second child which makes us four..right now we are in no situation to move out .. is the apartment company violating any rules/law with regards to accepting tenants and do we have rights if they say that since we are now going to be 4 in our family we have to move out.