For a long time, yes. I often have many Emacs clients editing the same buffer(s). It works reasonably well.

Not sure if there's been a way to integrate separate emacs processes, but it has always been possible to launch a new frame (emacs speak for window) displaying the same buffer, and given network transparency in X, have it displayed on any remote computer running X.

You can run an emacs server and operate out over ssh, if you want, sharing the buffers across many remote clients.

https://www.gnu.org/software/emacs/manual/html_node/emacs/Em...

Although if you're doing remote editing you probably want to use Tramp.

https://www.gnu.org/software/tramp/