I am willing to keep up with the emails to show I legitimately care about their reception!
I however would do the following.....
Could I call you sometime when you're not busy to get a better idea of what you would expect from an event??
If they answer no.....
I would send them an email..reminding them, that my dates fill fast, and if they want to "ensure" their booking, they better act fast! I would say, even if we had a meeting to let you two get a feel of what I am about! Get to know my personality, see if you "like" me!
If emails continued, and I thought they were "playing" with my dates...I would email them, saying another couple has "inquired" about that date...but I told them that "you" had first chance at it! I have done this once before when a couple was on the fence! And we met, and they booked me!
Its a "dirty" trick...but I want to know who is "genuine" and whos "wasting" my time!
My time is important to me! If they are legetimate...they will "9 out of 10" times book you! Now this aint a true stat, but I know you catch my drift!