"Twenty families live here."
Translation:Venti famiglie vivono qui.
That depends on the order you used. A correct possibility is:"qui vivono venti famiglie" At the moment I cannot imagine another possibility.
Thinking a bit about this - there are sixteen ways of combining the four words. (Four squared) Many of the combinations would work in English poetry which just chucks words around in the order it wants most of the time! Turning it around, I actually find it hard to make a total nonsense of the words in any of the combinations. I think you have a great point of discussion here slawphilist.
In fact I am not sure about the rules for the order of words in Italian. My native language (German) is very flexible in that respect, Latin as I know even more (famous Cicero centences over a full page with the main verb at the very end). English as I learnt is much more rigid in that respect.