Is there any way we can have more than one Site Administrator than just one who can edit the site?

I've never tried it but it appears that you can make anyone you want an administrator. On the Mangage classmates under "Details" for the desired user there is a box to check to allow that user to have full rights for modifications to the site.
dp

Yes, you can. I have a total of four admins for my class site, myself and one representative for each class. I handle the bulk of the admin functions, but have taught the others how to add classmates to their respective classes.

You can grant admin functions to an existing classmate by editing their profile details, just below 'Show On Class List'.