Before creating any portals select all of the brushes and make sure their brush type is set to Structural. To create a portal just make a cube inside any and all of the openings on the Church. With the cubes selected in the properties panel/object under brush type select portal.

    To test the portals export the object and then load it into a map after being re-light the interior should look the same as it did in constructor while viewing the file under Dynamic mode. Also check the collisions if they are not working go back into constructor select all of the objects except the portals and change the brush type to collision then change them back, this should fix it.

    Your Church should look something like this.