Am I obliged to pay the subscription fees for the players who train in the bodybuilding gym but do not pay the subscription?

If the tenants refrain from paying the subscription unjustly, you are not obligated to pay it on their behalf, for their action is a sinful transgression. However, if their non-payment is a result of your overlooking or neglecting to collect the rent, then you are obligated to pay it to its owner, and you may seek reimbursement from them for what you have paid. A private employee is not responsible for the employer's money in his possession except in cases of transgression or negligence.