1) ONE party = less party expense. Bounce houses/moon walks are expensive to buy and just as costly to rent, especially when you have multiple active kids. When they were "in to" bounce houses, we only had that expense once a year, so renting one ($150+) wasn't so bad.
2) TWO cakes = individuality. As the boys get older, even though they share a party, they will each have their own cakes...just a bit smaller. Since baking/decorating is my side business, it's not such an expense. Cakes can be pricey. I guess learning to bake & decorate pays off.
3) Shared cakes = compromise. While the boys are young, they share birthday cakes. They alternate picking out cake designs and flavors. One year Ean gets to pick the design and Eli picks the flavor and vice versa. I try to design it in a way that they both have ownership. So far, so good...
Here are some of the cakes they've shared...
4) THREE sets of invitations...One for Ean's friends, one for Eli's friends, and one for family members. The invitations look identical except for the name is changed. I usually create and have them printed at WalMart. Using Photoshop, saving them as jpegs, and printing them as photos saves a lot! This year's invitations cost me $5 total...5 for each boy (10 total) and 12 combined for family. This means that Ean's friends don't feel obligated to get Eli something and vice versa.
5) Easy food...A few years ago, I discovered that I could boil up hot dogs, put them in buns, wrap them in aluminum foil, and put them in a cooler, and they're hot for hours! Then, a variety pack of chips and drink pouches in a cooler means I have very little clean up and everyone gets what they like. Sam's Club and Aldi are my friends!