They said it's because I did not follow the rules for marinating operation and deposits accounts at the bank.

@Brian Burke when you say year 2, do you mean 1 year from the time they deposited their capital?

I would not necessarily give up the deposit (if you have one) until a move-out inspection is performed so that there is some security for damages caused to the property.

All time periods affected by the Force Majeure event, including Closing Date, will be extended a reasonable time up to 7 days after the Force Majeure event no longer prevents performance under this Contract; provided, however, if such Force Majeure event continues to prevent performance under this Contract more than 30 days beyond Closing Date, then either party may terminate this Contract by delivering written notice to the other and the Deposit shall be refunded to Buyer, thereby releasing Buyer and Seller from all further obligations under this Contract.

Did you refund the whole security deposit or were there repairs?

Do they have pet deposits or pay pet rent?

In addition - checking account statements showing deposit income going back X number of months would also do that as well.  

It also states that any security deposit refunds owed will be made payable to all parties on the lease agreement.One tenant has stopped contacting the roommates and us, and we are not sure they are planning to return.

Deposit for another place + $ to actually pack up and move his stuff.

We offer early termination for basically all leases, which is 1 month plus the deposit if there's no damages.