Gratuity - X company is a sister concern of A Company - compulsory for the employee to resign from X Company?

Dear all experts. Greetings for the day..

Below is my query, pls help.

X company is a sister concern of A Company, If management is planning to transfer 1 employee from X Company to A Company,

Is it compulsory for the employee to resign from X Company?

Employee has worked in X Company for 5 Year and if he got transferred in A Company, will he/she eligible for gratuity?

Requesting you all for help.

Please refer to the discussion in this cite earlier >https://www.citehr.com/406987-gratuity-applicable-if-shifted-sister-concern.html#post1854432<