I apologize for the delayed response. I just started in this office on July, 1st and it has taken us all a few weeks to get everything transferred over to me. I double-checked your pictures and the swarm is called a False Cinch Bug (Nysius raphanus) if you want to look it up. They tend to swarm and as you have learned they love brassicas. 

They are likely gone this late in the season, but if you still have some issues or they come back, they can be blasted with water or a broom to knock them off the plants and some even suggest trapping them in trays of water placed on the ground around the plants. There is not a ton of data on treatments, but permethrins are effective and can be found organically, but with all chemicals, it is important to cover your skin and face. 

Please feel free to reach out via email if you wish to reach me quickly - <personal data hidden>