You can try setting a live trap and use eggs for bait, that way you can take the weasels and relocate them away from your house, or you can take wire and go under the bottom of your coop and leave a couple of feet on the outside and cover it with dirt. That way if they try to dig in, they hit the wire and can't dig through it to get inside the coop. Weasel proofing your coop will save your chickens.