Pee-pee twins

Devlin is not night time trained. He sleeps very soundly and does not feel the urge to empty his bladder. We've tried to waking him in the middle of the night to pee, but he refuses, and throws a tantrum about being woken up. His cries, of course, then wake the other two. He will, however, awake when his pull-up leaks. We do make him pee before bedtime at least twice. He usually doesn't have a drink in the last hour before sleep. But he still pees in the middle of the night. We will soon resort to more drastic measure, like taking away the pull up completely. But not yet. When the weather is warmer, and he can do with sleeping with only a light blanket to reduce the amount of laundry that will inevitably result.
Ceilidh, on the other hand, does not wet the bed. It's rare occasion if she pees in the middle of the night. In fact, she doesn't wear pull-ups at night. Even as an infant, she rarely wet her diaper at night, but filled it up within 30 minutes of waking in the morning. So, there was no real nighttime training with her. Her biology just led to nighttime dryness.
Once in a blue moon, she will wet the bed. When she's extremely tired. We had one of those nights when we were visiting the grandparents over the holidays. Ceilidh had stayed up late, watching movies with grandma. She was quite tired when she went to sleep. She also had a lot of milk before falling asleep.
The next day, Uncle Billy asked her what happened. Ceilidh shrugged, and answered, "I don't know. I just peed."
Uncle Billy pointed at her and Devlin and said, "You're definitely brother and sister - both peeing in bed."
Devlin piped up, "Well, we're twins, you know!"