Let there be none to extend mercy unto him - Let him find compassion and sympathy in no one. When he suffers, let him be left to bear it alone. Let there be none found to shed a tear of compassion over him, or to relieve him. Literally, “Let there be no one to draw out kindness to him.”
Neither let there be any to favor his fatherless children - To show them mercy or kindness. See the notes at Psalms 109:10.