If stepsiblings are asked to share bedrooms or other possessions, and one of them views such sharing as an intrusion, he or she may have difficulty overcoming the tendency to play the role of between his or her parent and the new stepmother or stepfather.

Divide et impera.

Explanation:

If one of the step-siblings views such sharing as an intrusion, he or she may have difficulty overcoming the tendency to play the role of divide et impera between his or her parent and the new stepmother or stepfather. Intentionally creating disputes between his or her parent and the other member of the couple. Playing the role of divide and rule is used to maintain control by dividing the concentration of power into units that are less powerful and easier to control than when they are together.

of what agreement it does not show

you so !