last year i had 4 interview offers for the same weekend. I managed to interview with all of them, though I let all the schools know about my weird circumstance. It went like this:
phone interview with School A Thursday afternoon,
flew to School B right after the phone interview Thursday evening and interviewed all day Friday,
flew to School C Saturday morning (6 AM flight), interviewed all day Saturday,
rented a car and drove to school D Sunday and interviewed Monday morning, then flew back home Monday afternoon.
While waiting in the airport to fly home, I received my acceptance from School C.
The point of the story is that it can happen, and schools are definitely willing to work with you. Be honest and they'll appreciate it.
sidenote: I ended up at School E so the weekend from hell was pointless. ha! go figure...