Update - US made it right
Update - Was pleasantly surprised today to get a call from US. Someone named Paul in their Airport Customer Service Policies and Procedures group. He told me that he had seen my post on Flyertalk and was able to secure seat assignments for my family. He explained the issue with the equipment change and was very understanding of how frustrating the whole issue had been. Lo and behold, I checked our seat assignments on the website and we now have 16A & 16B and 19A & 19B.
Kudos to US for making this right. And a special thanks to Paul for going out of his way to help!