This is effective likely to involve setting up a small private cluster for yourself, accessing these other machines. Whether this will is theoretically possible will depend on your network and the permissions that whoever administrates your colleagues machines is willing to give you. If you have a series of linux machines which can see and SSH to each other across your local network, then you are well set, and will find multiple walkthroughs online, depending on chosen tool stack. If these are all heavily firewalled Windows machines you don't have administrator rights on and can't install new software on, then you may be out of luck.
I've not used Ray personally, but it seems to come with believable installation instructions (see the private cluster section here). I have experimented with Dask in similar circumstances, and it worked out ok. Overall, though there are social difficulties taking compute time on multiple machines 'owned' a local user and networks tend not to be as fast as on dedicated clusters. In many cases the lo-tech solution of SSHing into a friend's machine and running one copy of an embarrassingly parallel task is an easier solution.