If all three signed the rental agreement, then you likely can issue the refund check to any of them or, the safest route, is to issue one check with all three names on it and mail to any one of them; let them worry about how they split it. I would not recommend your splitting it and issuing three different checks. You presumably don't know for sure if they all contributed to it equally or, if you are charging them for any damages and only issuing a check for the balance, you don't know how they intend to allocate those damages amongst themselves. If you split it equally, you may be overpaying one while underpaying another - and then you could be liable to those underpaid. How it is split is their problem, not yours. Good luck.
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