Live tracking app

need to track all my staff who works outside office , specially they deliver medicine to my customers , so i can track them and share their location to customers if they ask. i need to see how many km they travel because based on it i will pay them conveyance . all users details are saved in our sql database , you have to use it and store data on our database too. in app there will be two buttons login and logout when staff login then their track will be start and admin can see his live location and when staff logout his track will be off. you have to provide api so that i can integrate in our other existing desktop application too