Grilled steak and potato kebabs

INGREDIENTS

• 2 cup(s) fresh mint leaves
• 1 cup(s) fresh parsley leaves
• 1/2 cup(s) extra-virgin olive oil
• 2 - 3 clove(s) garlic
• 2 tablespoon(s) red wine vinegar
• 2 tablespoon(s) lemon juice
• 1 1/2 teaspoon(s) ground sumac or lemon zest
• 1 - 2 shallots
• 1 teaspoon(s) red pepper flakes
• 6 - 8 red or yellow new potatoes
• 4 tablespoon(s) olive oil, divided
• 1 1/4 pound(s) tenderloin or sirloin