My grandson is 12 years old and is controlling his parents.
He is fine when everything is going his way, but the minute he's ask to do something he doesn't want he really puts up a fuss.

When he's in your house, deal with it the way you want.

When he's at home with his parents, butt out.

When your kids ask for parenting advice, offer it then and only then. The advice I would offer them (when asked) is that:

• the child needs to know who is in charge, pitching a tantrum at 12 should be laughed at, not given in to
• that keeping QUIET in the house is never the goal, keeping respectful safety and order is
• clear rules, predefined punishments, calmly levied no matter how mad he gets
• take care not to levy a punishment against once-in-a-lifetime opportunities like proms and field trips
• it's way more important to be an unliked source of security to the child than it is to be his friend or to keep the peace

When things go wrong for the boy, either at home or away, he needs to know where he is safe... that happens by being firm now. That's the advice, delivered when asked.