It sounds like you need some consistency in all of this. It's gonna be key in setting up some kind of routine. I know it's tough because it sounds like the reason you give in is not because you think she's in any kind of distress (which, of course, she's not) but because you are trying to be fair to your other kids and you don't want their rest disturbed.
First come up with a bedtime you are comfortable with. You can even put her down before the other two kids so her acting out is less disruptive to them. It might help to give her about 20 minutes of undivided attention. After she bathes and is ready for bed, read to her, talk about her day for about 15 minutes and then give her 5 minutes for just back rubbing and affection. Then a hug and a kiss and leave the room. I would make sure there is a drink by them bed (a small ammount of water in a spill proof cup) and that she has gone to the bathroom. I would use an egg timer and set it for the 20 minutes so that she knows there is a finite ammount of time and that is it. Then let her fuss. It's the fact that you go in eventually that gives her that ability to go the distance. In her mind she's thinking, "Eventually....."
When she wakes up in the middle of the night, make sure that how you handle that is the same thing every time. Put her back to bed in as unstimulating a way as possible. It's not about ignoring her as much as it is about not engaging her and that really active little brain she has. Don't speak, or make eye contact. Put her back to bed and walk away. If she disrupts the others make sure you deal with THEM and not her. She shouldn't get attention for negative behavior. That's what she's wanting so that is the last thing she should get because even if it's negative attention it's a payoff. Reward her good behavior and her efforts lavishly. Make sure that attention she is seeking is given to her for all the right reasons.
Let her know that she is going to bed earlier so that she doesn't bother her siblings and that if she wants to stay up as late as they do she is going to have to go to sleep cooperatively and quietly.
Hope this helps,