INHO, it is a waste of time to try to respond to this nonsense. People who believe this stuff are too far gone to respond to any logical arguments. Anything you say to disprove their theories only confirms they are right.
If these are just FB friends I would not respond and probably “unfriend”. If these are friends or coworkers in the real world, I would limit my contact with them to the most superficial conversations. If they are family, I would also do the same and set strong boundaries, especially in my home and tell them if they spew this nonsense they have to leave.
I would pray for them.