We booked a round trip on Insel, they contracted with EZ Air. This plane is tiny, rickety, and seems worn out.

The real question is, does Insel actually have their own planes or do they just contract with others to fly their passengers.

Both. Depending upon the day/time, Insel contracts Easy Air's planes, though with Insel expanding their fleet, this practice may diminish. I've flown Easy Air quite a few times & have found their planes to be just fine (at least as good as Divi's, IMO).