Destroy the oil fields they control in Iraq. They are making millions of dollars a day and are financing a lot of things with this money.
Arm the Kurds and any Christian militias that are left.
Bomb their mosques. Kill their religious/political leaders.
The problem with the migrants is there is no way to verify any information on them. Whatever they tell you their name is you have no way of knowing if it's true or not. Send them back unless you can verify (how) that they are Christians fleeing persecution.
Should have been done a long time ago. Boots on the ground to mop up and take out their entire families.