I sugggest that you consider how you would feel if you were your Realtor. If the Realtor is the cause of the buyers coming to rent, then in our market (Atlanta may be different) typically a one year lease would pay the Realtor 5-10% of the gross lease amount as a commission. This arrangement would be in a formal written contract.
It sounds as though this is part of you had listing agent involved and an agent representing the buyer. If the buyers cannot sell their home, it sounds as though they may be long term renters until their home sells, is that correct? But the length of time it will take for their home to sell will exceed the length of the the current sales contract.
IMHO if the buyers are paying rent, and they end up not buying the property, then some form of compensation would be fair to both Realtors (meaning that you have decided to take your property off the market and rent it out).
I don't know your market, but if I were your Realtor and I had buyers occupying a property on a rental agreement, with an offer contingent on the buyer's home selling, I would have suggested in a counter offer that the buyer's property listingn price be reduced 5% per week until the property sells (or something like that). Most markets in the US are seeing declining home values, so if the buyers were serious about selling, then the property, properly priced , will sell.
So the bigger question, aside from commission, is that if property values are declining, the buyer's home will sell, but at a lower price than they want, and if they decide to buy your home, it will sell for less. Most listing agreements have a protections clause which states that if the listing agent was the reason the buyers purchased the home, and do so within a certain time frame (the length varies, normally three to six months), then the agent is owed a commission. Once the period expires, techincally the agent would not be owed a commission. In your case, if the buyers are living there because of the Realtor's marketing efforts, then morally I would think that you would owe both agents commission (and of course they need to perform the transaction when the buyer's finally buy).
The bigger question is what is the buyer's Realtor doing to get their home sold if home values are declining? Just based on your post is sounds as though all parties would be better served if the buyers get their home sold and purchase yours