Use carpenters glue or a pva glue to glue the underside of your quoins to the outside edges of the doll house doors, lining up the quoins so that they protrude slightly (1/16 of an inch) beyond the door side edges to cover the hinge slightly. Make sure that you leave space at the top of your door to fit the cornice trim if you are using that. Clamp the quoins in place and leave to dry.
When the side quoins have dried, open the right hand side door (on your right when you are facing the dollhouse), and glue the center quoin in place on the door edge so that it protrudes 1/4 of an inch beyond the door. This quarter inch will cover the gap in the doors and make the doll house front look like it is a single piece.
If you built your dollhouse with equal sized doors, you may want to balance the front with a second piece of quoin on the same door, to make it appear that there is a protruding front section marked by the quoins.
