@Sherry189 If your desired guests are parents of a student who are coming for a visit with their child, increase your rates, set your nights to a three night minimum, or do not do instant book.
This is YOUR property and you have the right to decline anyone that you are concerned is not going to be a good guest. If guests have to submit a Request to Book, you will have the opportunity to communicate. Do not be concerned that not being on instant book is going to tank your bookings -- if you want responsible adults and not party animals, the delay in booking via the request should actually garner better bookings.