Sharing a content root

My company maintains a monorepo with the following file structure:

monorepo/
  common/
  service_a/
  service_b/

Each of the services (a and b) depend on common by way of listing it as a project dependency in their build.gradle files. In service_a and service_b, you'll see the following:

dependencies {
  api project(path: "common", configuration: "default")
  //... other dependencies
}

This works fine. Each of the services builds as expected.

When I open service_a or service_b as separate projects in intellij, all of the dependencies resolve as expected. I can jump to the definition of sources in common from both service_a or service_b code. The only problem with this approach is that I now have multiple windows open, one for service_a, service_b, and common.

What I'd like to do is just open the monorepo directory as a project, so that I can see all of my code in one window. Additionally, when I'm looking at service_a or service_b code, I'd like all dependencies to resolve, and to be able to jump to the definition of common code from my service code.

What happens now is the following: I import monorepo as an existing project from sources. IntelliJ spins for a while indexing, and eventually leaves me with a bunch of unresolved dependencies in each of the services, save for one. The one service that the dependencies are resolved for is (typically) service_a (the first service listed alphabetically) - within code for service_a, common code is resolved. I can jump to definitions, see sources, etc. For the rest of the services, I get a bunch of "Unresolved reference" errors in IntelliJ.

When I open my project structure, I see that the common module listed among the modules in the project. I've tried going to each of the services and adding common as a dependency, but then I get the error "Two modules in a project cannot share the same content root".

How can I achieve what I want? Namely, being able to have multiple projects in the same window, all of which share a content root, and having all of the project dependencies resolve without issue?