Another Marauders related chapter, I just can't help it.

When James is grounded, he can come up with any excuse to let his mother allow him to use his wand and go out so there is only one possible way in which Mrs Potter can ground him and make him repent for it:
"No Sirius."
"What? What do you mean by no Sirius?"
"You are not allowed to talk to him, prank with him or interact in any kind with him."
"But Mom..."
"I said NO SIRIUS! James Potter, you're officially grounded."

Remus hardly ever does anything that could get him grounded but if the need actually arises, it is very easy for Mrs Lupin.
"Remus, you're grounded."
And Remus would groan in disappointment and empty all of his chocolate stock and put it in the kitchen cabinet under a heavy lock.

When Peter is grounded (and it happens very often), his parents would take his owl into custody and not give him any of the mail that is addressed to him by his friends.

As for Sirius, he is always grounded when at his parent's house. Every second he spends there is under confinement because he is such an absolute disgrace in the eyes of his family. No owl, no wand, no stepping out the room and no Regulus. Yes, you heard it right: no Regulus. (Poor Reg always tried his best to be on the good side of his family as well as his elder brother who had always looked after him when he was young).