If I am understanding the situation correctly you moved in one family with another family. Then when you had the combined family set to move they all moved to a different lot.
If that's the case, that's how it's suppose to work. If you don't want that to happen you need to split the combined family up via Edit town.
Select Split household and highlight each Sim you want to be moved out.
Click the arrow to move them into their own household. They'll be moved to the clipboard so you can then place them into their own house.