Waitlist mind games

so I am from Midwest, and have been waitlisted at 5 solid programs on East Coast.

1. What's the protocol for being on waitlist? Do I have to email them back that I am interested? Personally, I don't think it should help, but I don't want to be the only one who did not reply back.

2. I either have only one date available for those interviews or already have a interview scheduled for their dates. Do I let them know that..or is there a nice way to let them know that without sounding presumptuous? I am obviously interested in their programs and will cancel interviews for some of them.

1)I'm not sure if letting them know helps.... but I did let them know.

2) I personally wouldn't mention other interviews.. that's my opinion. but speak to other students, residents or attendings.