The blogs authentication is currently tied to the LAs instance.
If you are creating a blog where the members will come from different Local Authorities it is best to make it on the central /glowblogs instance.
Otherwise the users from different LAs need to have the the tile for the Glow Blogs of the LA to be activated. This can be done by their establishment’s RM Unify admin. You can then get access to authenticate on blogs on the LA that has been activated.
Here is a quick guide to Activating a Glow Blogs tile (pdf) for Unify Admins.
Alternativly you could move your blog to the central instance by exporting and importing it there.
Public blogs can be viewed by anyone, but you will need to go through a similar process is you have a private or glow only blog that you want members from other LAs to view.