Meh. Going around in circles. Well, at least I explored some options...
1. Invite-Only Access
This was my first resort, but I overlooked the following initially:
Apparently, admin/authors also count as "readers". So there are only 99 possible invites. Assuming I reserve some invites for my clan, I will still have to share the remaining invites between Sword 2 and sGE readers. After one day, my IAH forum inbox is already almost full. Too many innocent people will get screwed over with this.
2. Move To Other Hosts
Exporting the blog is possible, but problematic due to broken links within the posts. Going through 600+ posts to fix them? I think not. Also, while Wordpress has a nice built-in content control (see Page Visibility), it doesn't allow the user to edit/save CSS stylesheet without paying. I can't even adjust the width of the post column, so my existing pictures will get cropped off. This is way too much work. No time to do this properly.
I suppose there just isn't a perfect solution. Anyway, I'm still not too comfortable with restricting a large group of people over a few individuals. So I'm going to reopen the blog to public access despite all the nonsense, and maybe limit selected future posts with text encryption. (Too lazy to edit old posts for now.) The latter will help a bit with self-censorship issues.
The question of how to circulate the passwords remain though. I thought of using forum private message, but IAH forums only allow a message to be sent to a maximum of 2 recipients. Maybe I will use the e-mail addresses I received so far for a mailing list instead. I will think about it some more before deciding. In any case, the passwords are not to be circulated without my permission. Otherwise, I won't send them to you anymore.
I hope this will be okay for most people. Sorry for the inconvenience caused over the past few days.