i simply put resource in another folder so for example my robot structure is
/project1/resource.robot
/project1/area1/test1.robot
/project1/area1/test2.robot
/project1/area1/test3.robot
in test1.robot test2.robot and test3.robot i put
Resource ../resource.robot
and then with robot area1 , robot will execute test1,2,3 and every test can access resource.robot