carry on as you are, and each and every time one of them gets down, then put them on the stairs. I had to resort to doing that (tis my 'punishment' when they play up...altho they usually get a warning first).
Well, if stairs don't work for you, then do what ever you would normally do when they play up other times.
and be consistent. That is something we always have to be sure of.....consistency is the key.
they will realise soon enough that it isn't worth it if they want good, hot/warm food.
EG.....say for instance DS1 is throwing food....
ask him to stop, and tell him why it is wrong (rude, unnacceptable etc....).then tell him that if he continues then X will happen.
if he does it again, then do X (for however many mins x their age), and then before he is allowed back then insist on an apology.
if he then continues, then (in my house) DS is sent away for twice the time, and his dinner is taken away.
he may then sit back down and finish his dinner when all other have finished and left the table...meaning he has missed out on the family time, and quite possibly dinner is past it's best.
It may sound harsh, I don't know how discipline works in your house, but for us, this works, and we very rarely have a ruined dinner.
to be honest, i make sure they eat properly at home if only because I want to be able to eat out with them and know they will behave! And they do.
HTH