As you described them, these "contracts" are Installment Sales and need to be reported in the year the contract is first executed. File Form 6252, and continue filing this form every year until the contract is completed or until the buyer defaults.
Individuals are cash-basis taxpayers and the S-corp's earnings are reported on your individual return. You receive principal, a gain-portion and an interest-component of income every year from these contracts. You are subject to tax on the gain portion & interest income in the year received.
Once you enter into a contract for sale, the buyer has legal rights to the property - it ceases to be inventory. The fact that you are holding the title as security and there may be some uncertainty about the buyers fulfilling their obligations, doesn't change the fact that there has been a sale. As a result of that sale, you receive payments and some portion of those payments represent current interest income and current gain on sale.
Report your installment sale in TurboTax Premier under Less Common Income, Installment Sales.
