we've just been through this too, I think we're coming out the other side, but am still a bit sleep deprived, so forgive me if I ramble...
ds (dc#4) was 2 two weeks ago and before Christmas had got to the point that he was screaming the place down every night for at least an hour, sometimes 2 hours before finally going to sleep
In our case, we'd redecorated our room and have a lovely new bad and it seemed he'd decided he wanted to sleep in it too! I didn't mind too much, but DH wasn't prepared to put up with the kicking and wriggling, so we needed to get ds back into his own room.
He had been in a cot with a side removed and replaced with a bed guard. This meant he could get in and out, but didn't fall out.
In our case gradual retrest didn't work as he'd scream if we were in the room, out of the room, if we were both in the room, in fact if we were anywhere in the house or garden! He was disturbing his order sisters too One morning I found all three older girls playing on the PCs in the lounge at 3am as he'd woken the whole house up!
We tried lots of things, and had limited sucess with adding dd3 into ds's room (we figured seeing her go to sleep might show him what to do!). Somenights he'd jst lie next to her (asleep) screaming though! We got almost to the end of the Christmas holidays and moved her out as she's in reception and we didn't want her sleep distured before school.
In the end we put ds into his own single bed and adding a nightlight (colour changing thing that projects a bit onto the ceiling).
I think he might have been afraid of the dark as the nighlight has helped. Now he's a complete monster getting in and out of bed at bedtime, but he's stopped the screaming, which means stress levels are much lower and his sisters are getting disturbed much less.
I'll shut up waffling now! just try to remember that it's only a phase and it will get better