Multiple users accessing Excel file on shared folder.

I'm looking to have an excel file in a shared folder in a small network 5-10 users.

1) If multiple users access the file at the same time, it will only save the user who saved the file last, correct? Is there any way around this?

2) Is there any way of knowing that a user has the excel file opened? Is there a way to make it (in whatever way.. altering the folder, using excel, etc.) so that the user knows if another user has the file opened OR to block the user trying to access the already opened folder?

Thanks in Advance!
Dave