They can access most things already. All pages under the home, adventure log, and wiki pages. Characters & items both have a place where you can give the player control, yet the gm can also edit. If you want them to access everything, you can make them a co-gm under manage players.
killervp
"A God...Rebuilt":http://www.obsidianportal.com/campaigns/a-god-rebuilt
when you go into the game itself on the right it says manage members. From there all of your players currently in the game are at the top. Just promote who you want to co gm and they will have the same access you do. They can do most things like wiki edits and the like already but if you want them to have the same access this will do it.
Comments
killervp
"A God...Rebuilt":http://www.obsidianportal.com/campaigns/a-god-rebuilt
Just trying to help out.