.im just at my wits end we have tried time out taking toys smacking i even did PPP it only seems to work for a week or two then hes over it
ok, on the PPP thing only working for awhile....it doesn't matter that he is over it, YOU have to continue with it, come hell or high water. It may appear to work in the early stages, but then he will miss all the negative attention he is used to getting and will up the ante in the naughtiness stakes. Then you fall in a heap because its harder than it was before. This is the stage you have to push through and its tough
If you stand strong continually, stand by the boundaries (I find timeouts aren't always the right remedy myself) you set regardless of what is going on it WILL soak in.

One on one time is very, very valuable (I know its tricky with 3 kids around), but try to incorporate it into everyday life. My DS is AWESOME at peeling carrots, he is the carrot peeling King Of The Universe. Even if dinner doesn't call for carrots, it is his job to peel one for me. He stands on a chair whilst I do the prep peeling the carrot into a thin sliver happily chatting away. I explain every little thing I am doing because that holds his attention. Every so often he graduates to stirring something etc. I speak in a low voice and chase the others out of the kitchen because "M is my cooking helper" - so I'm turning the neg attention into pos.
At bedtime I thank him for his help with dinner and again point out what a good job he did with stirring the stock or whatever.

It did take awhile for him to really listen, but constantly speaking in a low, smiling voice helped him tune in to me.

I did PPP with dp, and what I learned was the consistency makes the difference. Do what you say you will do. Hold the boundaries, whatever they are, whatever the circumstance.
Dp is NOT consistent, always falls back into yelling and the result? The house is nuts and dp seems to have no control whatsoever.
I can handle DS fine. We have our 'thang', he's my boy and I always find ways to praise him for his ingenuity (even if it's nearly destroyed something!), then find a way he can do the same thing but in the backyard. Even breaking stuff. Hell, it's FUN, but you can't trash the house can you? Sometimes I give DS a couple of eggs so he can break, mangle, squash them in a bucket in the backyard
Everything he could bugger up (or use as a weapon) is waaaay out of his reach. This means I have to pull boxes down from high places often, but the house survives better this way

He really tires me out some days (yay for kinder!), but he KNOWS, I will follow through. He gets one warning "hit your sister again and no sweets". He stops straight away because I mean it - he went without sweets for nearly 2 weeks this month. If his dad says it he doesn't really care because dad gives in to the tears.....

Anyhoo - that's what works in this house. It's tiring sometimes, but if I make sure I can give him even 15 mins of undivided attention 2x times a day it makes the difference. He can have me to himself and not have to fight for it.

good luck! xoxoxoxo