I have not heard of the phrase "trial loan modification," from a bank. You will not be able to do a short sale and loan modification at the same time. There is a tremendous amount of risk with your clients' situation. If you know without a doubt that the clients will qualify and get approval from the bank for a short sale option, and the clients fully understand the risk and potential financial/credit consequences with no guarantee the house will sale with the option then they can make the right choice for them. Unfortunately, we as agents have little authority to make choices for the clients but are responsible for ensuring they fully understand the processes of what they want to pursue. Good luck to you!