I think a game camera would be a good idea for your set up, that way if some one was coming around you would have it on camera, make sure to keep your flock in a secure locked building if you can be there to watch for them. So sorry about your drake.
The drake feather is the biggest giveaway, but it just sounds like your girl is acting out the mating ritual. That's good they waited longer to start laying, gives them time to mature which I think is a plus since they will be laying eggs almost daily,.