I've been having the same issue, but with random families and sims, not clones. So far it's anything from singles to married couples with kids already, but mostly it's large volumes of single YAs in houses numbering 1-4. They don't seem to be filling any particular niches either, such as having specific jobs or roles in town. I haven't worked out why they're showing up yet.
Also seconding the everyone-in-town-is-fucking-around issue, but I haven't looked at their traits to see if this would be normal behaviour. I just assume my town is full of whores. VJ Alvi is a major player and I -know- that ugly bastard has bad traits. What traits determine likelihood to cheat? Commitment Issues and Flirty? (... Shouldn't this be in the main bug thread, by the way? Apologies for posting if so. )
I must get in and see if they are indeed flirty or such. However, it just seemed like such a large number of sims, so a large portion of the town must have some bad traits.