Because jet charter is not priced on a per person or ticket basis, it is not likely that it would be more cost effective for a group of 10-15 individuals to charter a jet compared with flying via scheduled airline service in coach or first class. Even if the total cost for a charter trip is split among 10 people, the cost each person would cover would still be significant.
Though the early Lockheed Jetstar had four, most production business jets have two jet engines, mostly rear-mounted podded engine. If mounted below their low wing, it wouldn't allow sufficient engine clearance without a too long landing gear. The HondaJet is the exception with its over the wing engine pods. Dassault Falcon still builds three-engine models derived from the Falcon 50, and the very light jet market has seen several single-engine design concepts and the introduction of the Cirrus Vision SF50 in 2016.