Is it obligatory to return the money to the club that was defrauded by two people entering with one ticket, and what is the way to do so without remembering the number of times?

If the party entitled to the money is present and accessible, the money must be delivered to them by any possible means, even if by postal transfer, bank deposit, or through an agent, and there is no need to disclose the reason for their entitlement.

If the exact amount of this right is unknown, the person obligated to pay must strive to estimate it to the best of their judgment, such that they believe they have fulfilled their obligation. This is because Sharia rulings are built upon غالب الظن (preponderant probabilities), as the Lawgiver has treated probability as certainty in the application of rulings, and probability is established in place of certainty due to its impossibility or difficulty in most situations.