I just gave both Lucas and Sebastian a bath at the same time. I had been putting it off because I was a little lazy. The idea of having to hold Lucas to make sure he doesn't fall off was a little dissuading. But it went okay. And they both had a blast. It's true that it cuts bedtime in half. Then again, Tiziano helped by dressing Lucas and giving him a bottle while I read to Sebastian.
Next step, dress them together, and read to them together.