How do wewe futa an existing family on the sims 3?

Haiiiii I want to futa one of my existing sim families so I have a house for another sim family I want to make. They only give each sim family 20,000 simoleons to start with to buy a house which is ridiculous.... And a lot of the houses are over 20,000 simoleons which sucks and I don't want to merge my new sim family with any other existing family. So can somebody help me? Thank you. :)