There is no such legal term "group company" or "group of companies" when more than one company is owned by the same individuals or a family. Every company is a separate legal entity in the eye of law unless and otherwise there is functional integrality or common balance sheet.. So when an employee borne on the rolls of one company is transferred to another, there should be a formal agreement between the two about the continuity of the services of the employee under transfer so as to avoid future questions like the one you've just raised. The employee concerned should be also informed about this fact in the orders of transfer or by any other means.If there is any insurance scheme regarding gratuity in both the companies with the same insurer, I am not sure about the formalities.If the transfer is a permanent arrangement, it would be better to settle the gratuity for the services rendered in the transferor company by itself.
From India, Salem