Luevano is good, but he does not fight the wa Mtagwa does. His chin can't take as much heat in the pocket. He'll try to counter Lopez, but is just not in his class. Lopez by KO.
Gamboa-Mtagwa is a bit more interesting. If his speed and power aren't enough to get Mtagwa out of there early, Mtagwa will keep coming and coming till something gives. Gamboa's history of flash knockdowns notwithstanding, I don't see him losing by T/KO. I see a small chance Mtagwa will get this by D, but the safer bet is Gamboa by KO.