Buggy reccomendations for twins & 17m old?!

[MrsY87]

We have recently found out we are expecting twins which will be DC3&4! When they arrive DD will be 4.5 so capable of walking despite being lazy and DS will be 17m so won't be capable of walking long distances. I'm thinking one twin will go in a sling (probably an ergo) the other twin in a double buggy along with DS. DS will
Be at nursery some days so I want a buggy which I can easily swap between being a double for the twins and a double for a twin & DS. Ideally a travel system so I can pop a car seat or two on the frame as well for nursery drop offs etc.
I've looked at the Donkey but not sure how easy it will be to swap between carrycot & seat as they use the same seat frame. I've also looked at the vista which looks like it would work perhaps more easily but I have heard they can be hard to push in double mode. Any recommendations for these or any other doubles I should consider!?

I have a donkey and love it. It does indeed use the same frame but it wouldn't take a minute to change if necessary as it is Velcro that holds the seat:carrycot to the frame so easy to undo in my opinion. I also love that I can have my dc facing different ways and that they both get a good view of the world. Unlike some of these pushchairs where the baby sits under the seat of the older child.

I've been looking at the ABC adventure buggy, it can be turned from a quad to a triple then to a double, it's Australian but u can buy them second hand on eBay, I'm currently on the look out for one as I have four children, 5, 3, 2, 9m and I also have a 5th child due in January