Sanasun,
I'd love to answer your question, and I really enjoy talking about the challenge and how everything works, so don't worry about asking, on the contrary, I think it is great.
Ok, let us say that I will change from the d'Angerville household to the Monk household, this is how I do it, step by step:
1. I save the game
2. Then I go to "Map View" and go to the Monk family
3. I left-click on the "house"-icon for the Monk family
http://ofkingsandcastles.files.wordpress.com/2014/02/changehousehold01.jpg?w=640
4. 3 options appear, "Visit the Monk household", "Visit the Monk household with..." and "nraas". I pick "nraas"
http://ofkingsandcastles.files.wordpress.com/2014/02/changehousehold02.jpg?w=640
5. A new menu shows up with the option "Story progression", which I pick
6. A pop up is displayed with the option "Make active (Dream Catcher)", which I pick
http://ofkingsandcastles.files.wordpress.com/2014/02/changehousehold03.jpg?w=640
7. Now Nraas changes the active household so I am now controlling the Monk family
8. I go to "Map View" again
9. I go to household of the d'Angerville family and left click on it
10. I pick "Nraas" from the 3 options
11. I pick "Story Progression"
12. In the menu I pick "Lot options"
13. I now click on "Allow For Lot Progression" and click on the check-button at the bottom right. The menu should now display "Allow Lot For Progression False"
http://ofkingsandcastles.files.wordpress.com/2014/02/changehousehold041.jpg?w=640
14. Still in "Lot Options", I select "Reset to default" on the menu, press the check-button and then select "Caste Manual" and then I should get the option "Active family Has" (observe that you do this step only if you have manually casted the "Active family" caste to start with, otherwise, disregard this step). Now the family should no longer have the "Active family" caste
http://ofkingsandcastles.files.wordpress.com/2014/02/changehousehold05.jpg?w=640
15. I now click on "Caste manual", in the "Lot Options" menu, I pick my "RKC non active family" caste. Notice that all my RKC families have the regular "Non active household" caste under "disallowed"
15. Now I am done with the d'Angerville family and I go back to the Monk household, still in "Map view". I go to the "Story Progression" menu and select "Lot Options"
16. I select "Allow Lot For Progression" and after I click the check-button it should say "Allow Lot For Progression True"
17. I select "Reset to default" on the menu, press the check-button and then select "Caste Manual" and then I should get the option "RKC Non-Active family Has". Press the check-button. Now the family should no longer have the "RKC Non-Active family" caste
18. I now click on "Caste manual", in the "Lot Options" menu, I pick my "Active family" caste. Now the Monk household should have the active family caste
19. I save to a new file (Save as...)
20. I go the main menu
21. I load the saved neighborhood (I do this because otherwise the aging does not trigger)
22. Done!
I hope this helps clarify things :D