What is the best answer to cross link one RTC instance to another and one development line team area to another?

We in Project 1 and Project 2 have the need to have user stories such as those below. (Notice there are two three levels of dependencies here - two within an RTC instance across development lines, one across RTC instances):

Project 1 instance:

Story: As a user, I want function BLUE
Task: Integration work to work with GREEN codebase from Team 1

Project 2 instance:

Team 1 Development line:

Story: As product ABC I want function GREEN
Task: Development work to code GREEN and work with RED codebase (that supports GREEN)

Team 2 Development line:

Story: As a GREEN user, I need RED functions
Task: Development work

For now, we're doing cheap things like noting informal handoffs and cross linking via http urls, but that isn't really the best answer.

Thoughts?

(Sorry if this seems confusing - it made more sense when the real function names were listed)