I have been playing the sims 3 since it first came out and I have completely run out of creative ideas for my sims families and lives. I usually create a family, get bored with them after a few days, ...
You could try having 2 opposite sisters/brothers/best friends etc. and see how it works out. You could have one sim be good and one sim be bad and try balancing and working with both. I loved playing these games so it should be okay. :)