Let's see if I understand your situation, @Mark1040 . For June 26-28, you want a guest to stay both nights, not just one night and you are willing to entice a 2 day stay with a discount. However, you are willing to accept one night for each night with no discount. Is that right? Not sure there is a way to do that but let me know if I am right.
If you only want a 2 day stay and do not want two single night stays, then you could reduce the nightly rate for those two days, and add the special requirement of 2 day stay for that period of time.