Thanks for all your great replies girls! Good to know I'm not alone. Firstly, we're in Melbourne, and would love catch up's with other large families!
Yes, have to try and address the issue. The problem is most of these people are DH's relatives or friends. I've put a lot of pressure on him now to confront the issue with these people as the problem's not going away.
It's funny, but you smaller family mums say what many of our (nicer) friends say when we either come to visit or they visit us: that our kids are like a great rent-a-crowd. They entertain their kids no end. The mums are forever badgering me to give them tips on how to make their own kids better behaved as mine have such good manners.