This morning I updated my Chromebook and, when I rebooted into the new image I noticed these accounts had appeared. Probably some special development things. Like the Super User account I get, but what are the other 2 for?
I’m not sure what those account are but it’s a known issue and it will be fixed with the next update.
I have the same issue and I suppose it was caused by this commit (already fixed). Should resolve in next build, I guess.