Since your establishment is an exempted establishment, the manner in which membership is allowed, etc., will be according to the Trust Deed. Please refer to the trust guidelines. The rules and regulations of the Provident Fund Trust of the exempted establishments will differ from establishment to establishment. Therefore, we are not in a position to give you advice just based on the plain reading of the post.
In the case of employees who have joined your establishment after having worked in other unexempted establishments, you have to provide them coverage even if their salary is more than Rs 15,000. This is strictly dependent on the Trust Guidelines, but I am afraid there is no chance of getting any exception from the coverage of the PF Act if your establishment's PF Trust guidelines state that no employee can join PF if their salary is over Rs 15,000. Normally, the PF authorities will grant an exception only when the scheme of your own PF is better than that of the Employees' Provident Fund Organisation. Therefore, please refer to the deed in detail and get back to us.