Make an announcement they can leave now with all their loot, families, etc. intact, even apply for legal re-entry when it is their turn on way out. If they are apprehended after the cut off date it is "Go to deportation, do not pass go, do not collect $200"
Straight to deportation across Mexican border, no appeals, no delay, no fucking caring about any distress the actions of the illegals have brought upon themselves after being generously warned. All their loot forfeit. DNA sample taken and no member of their family may ever enter United States for 100 years minimum.
If that doesn't motivate them to fuck off on their own, then they truly are the kind of evil parasites you never want in this country and need at least 100 years for their descendants to have a chance to grow some honor.