yes, you can split meals as long as you're not buying meals for someone not on the plan. It is one way to stretch your dining plan, too. For example, if you were only there for 2 nights on the Dx, but were actually going to be in the parks for 3 days on your 2 nite stay, then you could use the 12 total meal credits like this...scenario is Magic Kingdom day 1, Epcot day 2 and Animal Kingdom day 3
Day 1 split lunch at Cosmic Ray's (credit 1), dinner at Cali Grill (credits 2-5)
Day 2 split breakfast at resort (credit 6), split lunch at Sunshine Seasons(credit 7), dinner at Coral Reef (credits 8 & 9)
Day 3 split breakfast at resort (credit 10), late lunch at Tusker House (credit 11 & 12)
You'd also have 8 snack credits to use in case you get hungry between meals, or need bottled water during the day.