Quadruple the dependencies

I’m working on a project with four — yep — four external dependencies. Each entity is writing some code, each entity is hosting some machines, each entity has its own deliverables.

There is no way to reduce the number of dependencies, for reasons that are more political than anything else.

I’m looking for resources — list of tips, schedule template, checklist of todos, etc. — to manage a multiple-dependency project. Anyone out there have anything?

Much thanks.