Since you two will be there early and you know how the roads are there, maybe get a smaller car for the two of you and add a car when the kids get there? Did pretty much that in St John in June to spread the group out and make driving the roads a lot easier. Definitely not as big a deal to follow someone than it is to find a van, I think!
Or hire a taxi for the day when the kids are around? Either way, it'll be fun!
Keep Smiling!!!
-Peter