How to get professors to reply to my email of inquiry for research opportunities / Co-Advising
EDIT: I did not see &quot;3 emails&quot; when I originally answered the question.  I thought we were talking about 1.
In light of that, it seems probable that they are not interested or don't have an opening. There is a chance they are just busy, but seems unlikely.  You could wait a month or so and e-mail again, but unlikely to get a different result.
You should either look for different professors, or start looking around for other schools that have good programs and email them.