1. is there a way to make the monday to friday schedule different than the saturday and sunday schedule?
You could create two separate shifts. Perhaps call one "Weekdays", where you would only schedule people on Monday through Friday
 and a second shift would be "Weekends".

          2. How can I schedule more than one person for the same shift?
MyRoster only allows one Shift Provider per shift. However a reasonable workaround would be to create multiple similar shifts, eg instead
of trying to place more than one person on a Shift called "Morning shift", You could instead create "Morning shift A", "Morning shift B" etc.

          3. If I delete a provider or shift, does it affect all the other entries from previous schedules?
Yes. Deleting a Shift or a Shift provider will delete older entries and will affect reporting for those schedules. We are working on changing this behavior.

4. The maximum number of users allowed is 25. What if need to add more?
The maximum number of users is limited per account, but there is no limit to the number of accounts an individual can have. So one way around this limitation 
would be to create multiple groups with at most 25 users. You can also use this to get around the maximum of 10 shifts per group.