Hi Ashok,
For the purpose of PF coverage, if the management is same or if there is a relationship between these 3 units means, then, you need to consider the total strength of 3 units. Also, remember to include the headcount of all the direct and indirect employees associated with the company. As per your query, it is clear that the management is the same for all the 3 units. Hence, count of all the 3 units to be considered.
Let me know, if you need more clarification on this.
Regards,
Srini