The Cross family are a premade, playable family, whom can be found in the neighborhood of Lunar Lakes. It consists of Patricia and Alexander Cross, who are married but are drifting apart because of their focus on work, and their lack of romance.
Patricia and Alexander share their last name with the founder of Lunar Lakes, Anthony Cross. Whether or not they are related is unknown and up to players to decide, though Patricia's bio on The Sims 3 website states that she is a direct descendant of Anthony.
They share their surname with Miriam Cross, a social worker in the world, and are likely descents of Odessa Cross from Barnacle Bay, as most sims from Lunar Lakes are descended from other pre-existing SimNation sims.