Links ladies, I want links! 
I like those floor beds muck , but I don't love them..
Hmm, is your DN still having a nap in the daytime? If so, cut it down until shes sleeping at night.
We've been there with DD2, bedtime was just hours of brilliant fun for her - we tried the 'back to bed' technique (Supernanny) - of simply not uttering a word and taking them back to their bed. When DC senses any anger/frustration etc, it makes them 10X worse, so the key is to stay emotionless.
It half worked for DD2, but still took us a long time - she is soo stubborn, but I image a 2.5YO would give in sooner.
Have they tried sitting in her room? First few nights you can sit on the end of their bed til they've settled, and then you gradually work towards the door, until 1 night you sit outside.
We did a technique with DD2 with books - I would think that your DN is too young, but its still an idea. We basically sat her in our spare bedroom (nothing in there but a bed and furniture) with 5 books and said that she can choose when she wants to go to bed. We had our doubts as the first night she stayed up until about 10.30pm, but went to bed with no fuss at all - a total winner for us as no technique had worked up until now. Gradually she would get more and more bored and choose to go to bed earlier.
With DD2 we found that a technique would work brilliantly for a few months/weeks and then she would start being silly again.
One thing I might suggest, just to break the cycle, is that your DBro leaves your DN up at night until maybe 10/10.30ish (bearing in mind they've cut out the nap) or basically until she is literally falling asleep standing up - then take her up to bed. She'll be so tired that she should just go straight to sleep. The next night she should be sooo tired, but again, keep her up until she is super tired and then put her to bed. Every few nights make it a bit earlier.
We definitely feel like the girls are ready soon - we're not going to go out tomorrow and buy them, but we'd like them to be in beds by the beginning of September.
Now E is back to her usual cheeky self, she might be a monkey at bedtime, but the only thing stopping her is being wired up to her feeding machine... so she can't physically get out anyway! Oh god, I sound so horrible, but its one less child who can be running around at night!
We may even keep the cots up, but in the spare room, and threaten that they will go back in if they mess around.
Looking forward to seeing some more beds being sold to me! 