It seems your age, working and all, definitely deserves a little privacy. No lock on the bathroom door? I would tell them politely that if they don’t mind, you will install locks on the bathroom and bedroom doors, you need your privacy.
If they don’t agree, start walking in on them.
Or when they’re using the bathroom stand outside and keep asking “What are you doing?”, “Is something wrong?”, “Can I come in?”.
I'm a big fan of 50 Cent, or as we call him in Zimbabwe, four hundred million dollars.