Understanding Jesus counter argument against the Pharisees (Luke 11:19 )

I don't understand the following counter argument by Jesus. > And if I by Beelzebul cast out demons, by whom do your sons cast them out? Luke 11:19 One viewpoint is that the Pharisees' students (which I believe is what Jesus meant when he said sons) did try to cast out demons, but that would mean that I would be assuming that the Pharisees' student did actually cast out demons during that time. 1) Would the aforementioned argument be valid? 2) Are there any other ways of understanding Luke 11:19? If yes, could someone please explain them?