G.
Well if you have tried everything and are open minded here is what I suggest. I would let him sleep with you. I suggest reading the Family Bed. You may have pushed him too hard (don't feel guilty). He sees his two younger sibs get different treatment and he is PISSED. He did not get enough babying from you and now wants to be babied. Instead of pushing him forward or trying to maintain what you have done LET HIM REGRESS, he needs to. Trust him, he knows what he needs. Life is not linear.
Hope this helps, I know it is frustrating. I went through some of the same things when my kids were little.
G.