I don't suggest you to install a house with a family in it, even twice only. You will produce duplicated sims, and it can damage your game.
Besides, it's more fun to create new sims in the CAS...
.
I downloaded once Lyla Grunt family, somebody revived, and by mistake planted the house in Strangetown. In Lyla's house, the General was already an elder, and Tank was a zombie. I looked at the SimPe, and Tank (still teen yet) indeed was an adult zombie, and the General (still adult yet) was an elder. Even when I moved the house to the lots bin, the characters remained the same.
I had to restore previous saved neighbourhood, to return things to the beginning.
From then on I never download houses with families in them. Only empty houses. But if you are more than interested in the house you downloaded, do as I said above - no cheats, no tricks, just little more work...
.