1. tell them openly and honestly. I'm sure they already know something is going on and the longer you keep from them the worse they think it is and the less they trust that you are telling them the truth.
2. 2 nights.
3. A robe is not very feasible or comfortable due to IVs and the nurse's incessant desire to take your vitals, including blood pressure. Take a button up rather than pullover shirt to wear home. The tube they put down your throat to keep your airways open while under anesthesia can cause your throat to feel scratchy for a few days so you might want to take some lozenges.