THis might seem a bit left of field, but what are their sleeping & eating habits like?
The behaviour you describe sounds very much like my DS when he hasn't had enough sleep or he's reacted to somethign he's eaten (i haven't narrowed it down, but I suspect certain food colourings/additives do it). Normally, he's quite reasonable and will listen to me, but when he's like this he just can't control himselfe. Everything is either incredibly hilarious or the absolute end of the world. It's awful - can't imagine having two going on like that.
And he'll change his clothes all the time too - what is with that?
Anyway, just a thought. Hopefully you'll get some better ideas here too - I have no idea what to do with DS when he's like this. Nothing gets through to him.