Hmm....I'm interested to know if your parents are
investing in your medical education. If they are paying a part or even all of your med school, I would think their tagging along is
kinda justified. I mean, hypothetically if someone was paying for me to go somewhere I would feel an obligation to show them what they are paying for. But then again, I have never been in such a situation so I'm not sure what the protocol is.
For your best interest I would speak up and tell them you prefer to go on your own and that you would interview better without their distraction.
If they must tag along it is not the end of the world. Speaking from experience, as someone who have had to venture off a lot on my own, having a companion along for the journey isn't so bad.