House Trained Dog Peeing and Pooping Inside?

My 5 year-old house trained dog has recently begun peeing and pooping inside the house. She usually does this when the parents of the house are gone, but the kids are home. She'll refuse to go outside or come right back inside after being drawn out with treats, then walk straight to the front door or stairs area and do her business. She has no medical issues as was confirmed with a recent checkup. The spots she goes have been cleaned thoroughly with pet cleaner and vinegar/water mix. How can we get her to stop doing this?