I do not know any expression. but this person can be called a mischief-maker ;

Macmillan Dictionary : someone who enjoys causing trouble or disagreement

I , of course , would prefer to use stirrer. it is a more exact but informal. it depends on your context.

Macmillan Dictionary : someone who tries to cause trouble between other people

I do not know any expression. but this person can be called a mischief-maker ;

Macmillan Dictionary : someone who enjoys causing trouble or disagreement

I , of course , would prefer to use stirrer. it is a more exact but informal. it depends on your context.

Macmillan Dictionary : someone who tries to cause trouble between other people

EDIT: I have found a appropriate expression: play sb/sth off against sb/sth

Collins Dictionary : If you play people off against each other, you make them compete or argue, so that you gain some advantage.

Example:Gregory would interview them, and would play one off against the other