Hi Peter,
Oh i see. It seems that it is not possible to set comment to specific user group only.
But it would be best if you can submit a feature request regarding this issues in our voice page ->
http://stackideas.com/voices, so everyone else could vote for it, the more people request on this, and we will priority consider it.
Suggestion:
Maybe you can set the first two blog to be accessible only to your assigned teamblog and 1 more to be accessible by everyone as shown
http://prntscr.com/czvw2f.
Those first 2 teamblog menu wont be accessible by guest and etc.
Hope this helps