In fact, it is quite normal in the private ESL industry (training centres) to teach ESL/EFL to a multinational audience with diverse linguistic native speaker backgrounds. Since English is the language of instruction, it should not be any particular problem, and I do neither know of any advantages nor disadvantages.

For the different ages of your students, there may be a problem if the differences are too big. But if all of them are adults, you should not have any particular problems either. So, I would not have too many headaches about it before actually starting to teach them.

The rest will be shown by time passing by. You will certainly make your experiences and can adjust your teaching styles and methodologies whenever there is a need.

Good luck!