June 2012 we went to a bank to notorize the contract. Before they signed it we talked it over and I asked them if they had any problems with the agreement. They said no and signed it. Their rent is due each month by the fifth. After they paid the 5000$ down payment I gave them 1 month to make their first payment. They paid in the middle of the month of July intending it to be the August payment. But did not send notice of its intent. However, every check came to us on the 20th of every month there after. I called them and explained the error. The buyers were suppose to buy insurance to cover the home loan in case. This was not done until I sent them a letter notifying them they have a penalty for not obtaining insurance. They finally obtained it. Is there any attorneys interested in this
To address the last part first, it sound like they got insurance but you had to remind them. Unless you were damaged by their failure (a claim arose while the home was uninsured, for example) this may bug you, but it is not an issue the courts will fix.
The wording of the contract controls the payments: if it clearly said $5000 down then a payment in July and monthly payments due on the 5th of each month thereafter, then I agree it sounds like they are behind one month. It will cost thousands to hire an attorney to prosecute a suit to recover that one month's payment: the court can award reasonable attorney's fees along with the missed payment and any contractual late fees or interest at the conclusion of the case if you win.
I wonder, and the judge will wonder, why you waited a year and a half. Breach of contract is enforceable up to 6 years, but if the defendants can show that you waived the breach, they would win and you would need to pay their attorney's fees.
The general advice above does not constitute an attorney-client relationship: you haven't hired me or given me confidential information by posting on this public forum, and my answer on this public forum does not constitute attorney-client advice.