Well, here's an update. We hardware clothed the coop and have been putting the remaining two adult chickens inside. We also put out a havahart trap, but each night the liver bait is gone with the trap closed. I'm wondering if a cat or fox got into the trap, ate the bait, and when the door closed, the door closed on the animal's back, and the animal simply wiggled out without any harm. I'm going to put the trap inside the chicken coop's run tonight, to eliminate the larger animals from getting to the bait.
No attacks in the past few nights as the chickens were inside the coop, until last night. The weasel somehow found a way inside the coop and killed and mostly ate one of the two chickens. I looked and I think I found a gap between the wall and the floor which was mostly covered in straw - that must be how it got in. I blocked that up but I'm wondering how many other holes exist.
I'm also wondering how good a climber the weasels are - can they climb up plywood walls? Can they jump to ledges and windows?