If your account is three months old it is eligible to apply to takeover an inactive coven. You will see links next to the covens name at the bottom of the groups page that says "apply to lead" or similar. If you do not see this link next to it, your account is not eligible to take over leadership of one of the inactive covens.
A member can only respond to an internal mail if they are online, next to a profile photo it displays when the member was last online.
The priest of the elemental magick coven hasn't been online since the 29th April 2015 and the priestess since the 10th April 2017, it is likely that they simply haven't got round to reading and responding to their coven applications yet as they are currently away from the site.