why cant two families on sims meet after i have made them

You basically have two options

Option 1: 

Load a family/Community lot of a lot that's in the same neighborhood as the one you want to move your family in.

Then click on the lot and choose Move in Household from the Gallery (the lot currently needs to have no Sims for the option to appear

Then you will be brought to the gallery/library screen. Choose the library and then the Household you want to move in

Second option is to click on the move in household through CAS from the map

You will be taken to CAS

Press on the library/gallery button and then on the library tab

Pick the household you want and place it into CAS (choose replace to replace the current CAS one)

The household will then be in CAS. Click on the OK button which takes you to the move in screen and you can place the family on the lot you want.