6
They are completely separate, unless you use an app that allows you do add two or more accounts and then merges your feeds. Downside is that you'll see duplicated threads if you subscribed with both, or are browsing /all.
The recent update from Thunder claims to eliminate duplicates though, see changelogs here: https://github.com/hjiangsu/thunder/releases
The app is already quite stable and useful, and comes for both Android and iOS (download below the description when you open the "assets" tab).
On desktop/browser I don't know of any way to make this work.