Soak the dry navy beans overnight in a large bowl, covered with water and 2" of headspace.
Drain the liquid from the peaches into the slow cooker with the beans. Then using a knife, cut the peaches inside the jar. Pour the peaches pieces in with the soaked beans.
Once soaked, drain and rinse. Transfer the soaked beans to the slow cooker insert. Add the ketchup, BBQ sauce, molasses, brown sugar, minced onion, and ground mustard. Pour in 2 1/2 cups of hot water. Gently stir to combine.
Set on low for 8 hours. Once cooked, stir in the tomato sauce (to thicken the sauce) and season with salt and pepper to taste.
Serve Slow Cooker Peachy BBQ Beans as side dish.