Creating a Pet for Pre-Existing Sims

In regards to your pets, I found things out through trial and error. In order to create pets you have to have a human Sim in the CAS with them, I tried to just do the pets without the Sim, but it would not let me accept the family without a human Sim.
What I found out you can do is create the new household with the Sim and the pets, and then you have to move them into a lot. What you do is go into edit households, and can move the pets between households. I bred a bunch of dogs, and used the main house as fodder, and then moved the offspring to the other families through edit household.
The bonus with it is that the original sim that had them still has a bond with them, and the pets are family they are still pretty much related. The game keeps track if a pet is a aunt/uncle/parent/grandparent, etc. Except for a few relations. Two dogs I have do have siblings that I bred together, and even though they are aunts to the offspring, they have no relation to each other.