Like Bernard Marie said, the Lead Link doesn't have the authority to mandate a process, you need to go to governance. There are different ways of achieving it. Two examples:
Example 1: A policy that describes the process that every circle member must follow.
Policy: All roles involved in software development and supporting activities must follow the Scrum process described below:
Example 2: A policy tied to a role. It gives you more flexibility when you want to update the process, as you don't need to propose changes to the policy in governance.
Policy: All roles involved in software development and supporting activities must follow the process defined by the Scrum Master role.
Role: Scrum Master
Accountability: Documenting and publishing a process ("Scrum process") to facilitate agile collaboration between software development related roles.
The tricky part with the policy is that you cannot mandate action from other roles, you can only restrict the way something gets done if the roles choose to engage in it. (see this Wiki page about policies for details). If you want to bring your specific case to one of our coaching sessions, we can look at it in more details.
UPDATE: I'm editing this post to add an Example 3 that would be more elegant and probably more appropriate.
First, Dien you could ask yourself the question: what is it that you want to expect from other roles? What activities specifically, and for which roles?
Instead of trying to use a Policy, you could try defining accountabilities on the circle roles for engaging in activities that you want to see happen as part of the Scrum process. For instance, you could define the roles so that you have a Product Owner, a Scrum Master, and a Developer role. Make those roles accountables for those things they're supposed to be doing according to Scrum. Give a domain to the Product Owner role for "Prioritization of the Product Development Queue" (or similar). In other words, bake in the rules of Scrum into your governance, by defining the roles accordingly. Does it make sense?
Lastly, remember that the Lead Link has a very limited set of authorities:
- Allocating resources inside the circle (financial, people time, ...)
- Prioritizing the work that circle members choose to take on (you can give a relative prioritization, e.g. project A is a higher priority than project B)
- Assigning people to roles, and remove people from roles.
- Choosing metrics for the circle that roles will report on
Hope that helps!