Well, sure, if you think it is easy, maybe it is–try it!
Do you want your sketch to send video TO facebook, or get video FROM Facebook? Very different. TO facebook is well-understood–they have an API. But I thought you wanted to load streams from facebook and process them in your sketch. Maybe I don’t understand what your sketch is supposed to do–you could explain more.
You might also consider looking at work by p5.js users who work with streaming video–for example, I believe that @lmccart does.
See also related discussions of point-to-point streams (non-platform), like