Only 4 of the 5 tenants have paid before move in. How to proceed?

[Alex Black]

I have 5 tenants that are on a joint lease schedule to move in on August 1st. One has not paid yet. How do I handle this situation? So far I've told them that no one can move in until rent has been paid.

More background information - All of the tenants are college students. I do my best to mitigate my risk by making the lease a joint lease and requiring co-signers for each of them. I require all my tenants to make payments through Avail.com. None of them have had any issue with this except one. I called the mother of the one who hasn't paid yet and her response was I sent a check through bank of america and it will arrive on or around the 1st. I explained to her that one, payment has to be received before move in and two, that all payments must be made through Avail and 3 I do not accept checks. I then asked her where she had bank of america mail the check to and she responded that she wasn't sure. I honestly think she lying about the whole BOA check thing. I reminded her that she agreed to this back in March when she signed the lease and she responded with a sarcastic OK and hung up on me. I've made all of the tenants aware that I haven't received payment from a 5th individual but none have responded. How should I proceed? What do I do about the four tenants that have paid. Since fall semester is starting back for students in this area in less than a month it is unlikely I find other tenants.