Why is moving out select sims so confusing?

I wish EA thought about this because I really want to split the household and without ruining relationships.

My sim's brother just had a baby with his wife and I want to move him, his wife and his son out of the house into THEIR OWN HOME.
For some reason that option isnt available. I can't figure out how to do it in CAS or whatever so I'm asking for help... again.

Hey! Open your map view, go to manage households, you'll see that some sort of window pops up, choose "manage all households", click on the family you want to manage, you'll see different options at bottom right corner of the window such as "Edit Household in CAS", "Move Household into a Lot", "Transfer Sims between families" and "Delete Household".

 Choose "Transfer Sims between families", another window opens (it's title so to speak is "Household split and merge") and you'll see your family on the left side of it and on the right side you'll see the option "Select a Household" or "Create a new family"(it's like an icon with + sign). If you choose the first option you can merge your family's selected sims with another family like the Goths for instance). If you choose the second one you can create a new family with the sims you selected (your sim's brother, his partner and the baby in your case). Then you can decide on what lot you want to place your new family and whatnot.

I hope I could help you