L.Z.
E.,
I don't think you should try to get them on the same track for now. If your baby goes to bed sooner, then I think that's great. That way once its your daughter's time to go to bed, he'll already be settled and asleep. Sending them to bed at once might just end up being too hard at first as they'll keep each other awake. Too much stimulation. You'll also probably be surprised at how easily your daughter will likely sleep through her brother stirring or waking up. Even if he awakens her, she'll likely be okay falling back asleep if like you say, she's always been a good sleeper.