Mission accomplished, on the widows. I left the kids alive. They are both Child stage and can survive on their own. I imagine they are eating a legendary dinner in the legendary dining hall, awaiting the new waterfall. The construction of the new waterfall has been unaccountably delayed by some kind of problem in the upper cistern ...
The first widow was the pig iron fan. She was easily duped into entering the fatal room. In fact, when it turned out to be leaky the first time she went back again to retrieve something she had dropped. Even though I left her body in there while I was repairing the lower level problems associated with the leak (no, gears are not watertight despite what I thought I read), it was able to be retrieved and placed in her tomb once I did drain the room.
The second widow was much cannier. When I relocated both her bedroom and her dining room into the fatal room, she began moving her items into her tomb. I locked the door to her tomb. She then went drinking. After a long while in the drinks stockpile, she finally picked up one of her items and went to her new "quarters". It was almost as if she knew what was going to happen. As I waited, I imagined a rather catty conversation between her and the true Duchess Consort, regarding her new "quarters" where she knew her predecessor had died.
As soon as she died, I opened the floodgate to drain the room. Her body had vanished. The outflow is filtered two levels down and captured some items, but there was no corpse even though the draining was done much more quickly than for the first one. Also, the game suddenly improved FPS. I am wondering if it was somehow bogged down by more than one Duchess Consort and took off as soon as I got rid of the second widow. I got my first Dwarven caravan in years, also.
I found it ironic that the dwarf who pulled the lever to drain the room the second time was none other than the Duke himself. I wonder if he is happy to be rid of two nagging consorts that were not even his.