Elena says that she and Sylvio traveled 12,000 miles. Other than using the incorrect standard of measurement given that they are from Greece which uses the metric system, the distance from Greece to San Francisco is actually closer to 6,600 miles.
Given that this is family reunion with their relatives from Greece, there is no explanation as to why Jesse's parents, Nick and Irene, are not at the house or the party.
DJ asks her maternal great-grandfather, Papouli, if she and Sylvio are related when Sylvio starts flirting with her. Papouli says they are not related. Later, this is proven to be false (although not legally speaking). Sylvio is brother to Elena who is culturally married to Jesse who is DJ's biological uncle.