If you have several deadlines approaching, you can play them against each other. Try writing each dean separately and asking for extensions. Be honest in your dilemma and tell them you need more time to decide be it because you haven't visited, you still haven't heard from schools, or some other legit reason. I believe they'll be likely to give you one since they want you bad enough to offer you scholarships...
I did it and it worked great...
Good luck.