duplicated sim(the SIMS 3)

[thesims3thesims3]

i created a new household(Presley) composing of 6 members. i placed them in a house near my "active household"(buena Vista) so that my active sims can easily interact with them. after a few sim days, they moved out (maybe because the house was so small for them) and bought a house near the beach. after that incident, i noticed that a sim of that household(Presley) was duplicated. i noticed that when i looked in the "relationships" tab.
One of the duplicated sims is the boyfriend of my active sim, while the other one is just an acquaintance. i though that was just a glitch in the "relationships" tab but i was surprised when they both appear in a party i threw. They look exactly the same. I dont know where the duplicated sim lives, but the original sim still lives with the Presley Household.
what might have caused this? is there anyway to delete the "fake" copy of that sim?

by the way, is it really impossible for teens to become siblings with young adults(or older ages) in CAS? the relationship available are only: "child" of and "housemate"