Once my wife was processing applications, said one guy looks good, and wanted to pay us part of the deposit to hold the rental until all the verifications are completed.

Do I send an acceptance letter to all 3 and whoever puts down the security deposit first? 

City of chicago has all sort of rules about security deposits.

So you might get rent and deposit before first payment due....or as you suggested might have to make 1 or 2 payments before rent starts coming in. 

He hasn't responded yet, nor deposited the rent as of 3pm on 2nd.

In regards to a deposit, I am used to longer term rentals so in a short stay like this what is typical?

The mail was dropped through a slot so the mail delivery person never noticed it piling up.

I cancelled the transaction and requested they sign a release of my deposit, (which was held at my attorney).

., odds and ends left in the house, no furniture), you can officially change the locks and take possession.Send a registered and regular mail letter to their last known address (your property) stating the abandonment and breaking of the lease, and keep the deposit.

"Loans Secured by Financial AssetsWhen a borrower uses his or her financial assets—life insurance policies, 401(k) accounts, individual retirement accounts, certificates of deposit, stocks, bonds, etc.