Sibling Rivalry

Hi,

Can anyone advise me on how to deal with a jelous 6 year old. The twins are
now 19 months old and his behaviour has just got worse since they were born.
He's really cheaky, won't go to bed all the usual stuff I suppose. I have
always been very good at routine but he seams to be very good at messing
things up. I've tried different approaches, being upset, being quiet,
shouting, smacking, taking things off him.... nothing works, he is really
quite good with the twins and they love him! Everyone he spends time
with.... without us, says what a good boy he is, school is very pleased with
him - who is this boy? I would like to see him once in a while.
I know this is probably normal but is there anything new to try and how long
will it last???
Luckily the babies are quite good, they sleep well - at least 12 hours a
night and they only fall out with eachother a little bit.
Anyone any suggestions, it would be really appreciated!!!

Tanya
Notts - England