In a medium bowl, mix the marinade ingredients together. Reserve 2 tablespoons of the marinade.
Place the Tenderloin Tips into a large plastic zip-tight bag and pour all but the reserved marinade over it, then seal and mix to coat well. Place in the refrigerator for 1-24 hours to marinate. This is also a good time to place wooden skewers in water to soak.
Boil the potatoes in a large pot of water until just tender enough to pierce with a fork, about 6-8 minutes. Drain well, then toss with 2 tablespoons of olive oil, rosemary, and mustard. Set aside.
Preheat grill to high heat while preparing the kabobs. Chop all vegetables into chunks that are roughly the same size as the cubed steak, keeping 2-3 layers of onion together in each chunk. Drizzle vegetables with the reserved marinade.
Alternate pieces of meat, vegetables, and potatoes until the skewers are filled, aiming for 5-6 pieces of steak on each skewer.
Place kabobs on the grill directly over the heat and reduce heat to medium-high. Grill for 6-8 minutes, flipping every 2-3 minutes, until the meat is cooked medium-rare to medium and the vegetables start to char just around the edges.
Remove from the grill and rest before serving.