Milton and Enriqueta didn't show up in The Sims 2 in Cassandra and Alexander's family tree. They didn't technically exist until The Sims 3 came out. They were most likely added to fill in as grandparents for Bella and Michael, just like Jocasta and Simis show up for grandparents of Cassandra and Alexander. Due to his traits, Inappropriate and Kleptomaniac, he was probably a bad father figure for Simis in The Sims 3.