My clients offer services that can be used by different types of organizations: schools, nonprofits, corporations, individuals, restaurants, etc. If I want to talk to all of their ____ simultaneously in a marketing comm., how could I address them?
“Stakeholder” would work for all the example organizations on your list except perhaps “individuals.”
Stakeholder
A person, group or organization that has interest or concern in an organization.
Stakeholders can affect or be affected by the organization's actions, objectives and policies. Some examples of key stakeholders are creditors, directors, employees, government (and its agencies), owners (shareholders), suppliers, unions, and the community from which the business draws its resources.
Not all stakeholders are equal. A company's customers are entitled to fair trading practices but they are not entitled to the same consideration as the company's employees.
(from Business Dictionary)
There are the terms symbiosis or symbiotic and mutualistic that refer to a mutually beneficial relationships.
