The first time I saw this trio they were in the middle of the road. I held up and waited for them to leave.
The second time they ran into a set of the Cenarian Outriders patrolling on their mounts. I jumped in and with the help of the Outriders took the three of them down. They are pretty strong, I think the Outriders would have been dead meat without my help.
Apparently the marauders are a quest. I guess I'll try that sometime. I now know how to take 'em down!