We're pretty tough on our DD at night - always have been. She's 3.5, and for the past year she's known that we're absolutely serious that nighttime is for sleeping unless there's a damned good reason for getting up.
I always explain that there are some things in this household that are non-negotiable, and one is that we MUST respect other peoples' need for sleep/rest. So for example, is is not okay to stand outside the room where your brother's sleeping and scream...nor is it okay to decide you're up for the day and playing at 6am. In bed, quiet, until 7am (barring toilet, sick, nightmare etc.).
All kids and all families are different though...what works for us doesn't necessarily work for you. Hope it's going okay tonight!