They're all superficial forks though. Without progress on the core engine etc upstream, they won't be able to keep up for long. On the other hand, there is little reason to think any of the three major engine efforts (Gecko, Webkit, Blink) are going to stumble any time soon.
For qutebrowser and Falkon, that's QtWebEngine, which you could call a fork of Chromium I guess - but it's more of a stripped-down Chromium with a stable API on top and a couple of patches. QtWebEngine is maintained by multiple people employed full-time by the Qt Company: https://wiki.qt.io/QtWebEngine
For Gnome Web, that's WebKitGTK, which is an official WebKit port (i.e. part of the upstream WebKit repository maintained by Apple and others) and also has been actively maintained for the past 13 years or so.