Just tell them your shift is over, nursing is 24/7, you've communicated what needs to be done to the oncoming nurse, have a good night/day! And then LEAVE. I mean it -- your shift is over and they can't compel you to stay. By staying when they tell you to, they are made to believe that they can
If you're getting in trouble for OT, I'm guessing the higher ups agree with you.
As for the complaining, sometimes ignoring it helps, and sometimes you just have to call them out on it. "Complaining doesn't get the work done," "we're not accomplishing anything here, and my shift is over/I have work to do," or if they have to help with tasks "Hey, it's the perfect opportunity to practice your brand new nursing skills! Don't want to lose those!
They do sound obnoxious. There's a bunch of those motivational posters on the wall at a local middle school, and one of my favorite quotes on one is "Leadership is action, not position."
Maybe you and your fellow floor nurses should take up a collection and buy them copies --
Leading at The Edge: Leadership Lessons from the Extraordinary Saga of Shackleton's Antarctic Expedition: Dennis N.T. Perkins, Margaret P. Holtman, Jillian B. Murphy: 9780814431948: Amazon.com: Books