The balloon impacted trees and terrain during a hard landing. Two passengers sustained serious injuries, and one passenger sustained minor injuries. The remaining passenger and the pilot were not injured. The pilot reported that the flight departed with three other balloons in light winds. He noted the wind was forecast to increase about one hour after the flight was scheduled to land. However, about halfway through the flight, the wind increased to approximately 11 miles-per-hour, with some gusts. He elected to land when he noticed the increase in the wind speed. He executed three approaches, each time electing to go-around due to adverse winds. On the accident approach, he intentionally brushed the top of a tree in order to slow the balloon. He briefed the passengers for a hard landing and descended toward an open field. After the initial impact, the basket became airborne again briefly before coming to rest. The pilot stated that he did not use the burner to reduce the descent rate due to the possibility of drifting past the selected landing area and striking power lines adjacent to the field.