Hi Rose,

I am really sorry for the delay of this reply. Please find my answers from your inquiries below.

1 . Can we disable the "task" ability for all the groups that in the easysocaial site ?

Yes you can. Go to your backend > easysocial > applications > search for "task" under group filter and then disable the task applications. Refer my screenshot here for better view, http://screencast.com/t/ohsudgH9HD .

2. Can we granting administrative authority to users that members of joomla administrator group ?

Currently only user that have super user status can be grant as administrator in EasySocial.