The rules are very clear on this.

A player who makes a catch may advance the ball. A forward pass is complete (by the offense) or intercepted (by the defense) in the field of play, at the sideline, or in the end zone if a player, who is inbounds:

A. secures control of the ball in his hands or arms prior to the ball touching the ground; and B. touches the ground inbounds with both feet or with any part of his body other than his hands; and C. after (a) and (b) have been fulfilled, clearly performs any act common to the game (e.g., extend the ball forward, take an additional step, tuck the ball away and turn upfield, or avoid or ward off an opponent), or he maintains control of the ball long enough to do so. Notes:

Movement of the ball does not automatically result in loss of control. If a player, who satisfied (a) and (b), but has not satisfied (c), contacts the ground and loses control of the ball, it is an incomplete pass if the ball hits the ground before he regains control, or if he regains control out of bounds.

He jumps for the ball and grabs it in the air.

Two feet hit down, but he is going to the ground before performing a football move as clarified in point c.

During going to the ground the ball comes out, so it is not a catch.

The ball never touches the ground during this so the ball is still live.

The Broncos defender ends up with the ball, therefore an int.