With the package sources listed in Package Centre you can do it from Synology Package Centre to get Homebridge and ffmpeg packages.
The Homebridge apps are just search plug-ins in Homebridge.
These are my Sources and packages:
Sources (Package Centre/Settings/Package Sources);
Homebridge https://synology.homebridge.io
SynoCommunity https://packages.syncommunity.com
From Homebridge Terminal;
homebridge@host:/volume1/homebridge $ npm list
homebridge@...
As this thread helped me to find the solution to running Homebridge, wanted to share my working solution.
The key change which helped to make it all work was adding ffmpeg to the video decoder setting.
Installed ffmpeg from https://packages.synocommunity.com/ - This seemed to work better than...