CAN ONE DEOMON CONTROL ANOTHER?

This is undoubtedly true.  Demons are completely devoid of love or respect for anything, including their own kind.  The have no ability to relate to each other or to the human world except through power and control.  If they work together for some purpose, it is only out of the most inveterate sense of self-interest, not because they have any fraternity or common cause with one another.  Their kingdom is strictly one of brute, loveless force which is maintained through a demonic game of survival of the fittest.

The demons' innate powers of intelligence and will make it possible for the stronger ones to dominate the weaker ones and even use them like slaves for their purposes.  It is very common for an exorcist to come up against demons that work as a pack but who are always dominated by one principle demon that is the strongest intellect and will of the group.  The challenge of the exorcist in these cases is to discern the identity of the individual demons, and to "divide and conquer" the band of demons.  The weaker demons are usually cast out first with the strongest one going last.  With perseverance and humility, demonic power can always be broken by the authority of the Church as long as it is correctly applied.

By Fr. Thomas J. Euteneuer "Exorcism and the Church Militant" page 44 question 29.