Great Idea! – you will see images throughout the site, I love joint birthday parties for children and it is a great way to share the costs. The only issue I have is that it is hard to make one child feel extra special when they are sharing a party (I have to be fair to all birthday Children).
I used to allow any number for a share, however I had to draw the line when one mum (not all hers) had 5 birthday children. There is a £10 surcharge per birthday child above two because I have to work much harder during tea (to secretly make extra prizes!!).