Take a look here http://www.eveonline.com/ingameboard.asp?a=topic&threadid=588918
for the roles. (point #5 I think).
Only those with a director role or "Config Starbase Equipment" role can unanchor stuff. so as long as the don't have that they can't unanchor stuff.
To give them access to the POS in general you need to tell them the Shield password or check the "Allow corp members" Check box on the control tower settings.
To be able to see/take from corp hangers they need the Hanger access - Other roles for those divisions.
I think you also need to set the access rights on each structure to allow access (right click tower -> Manage -> Structures -> Access). Though you will have to look into that.
Hope that helps.