Satyen, as I understand it, the employees are on deputation and thus, they continue to be employees of the Indian office.
Per RBI Foreign Exchange Management (Foreign currency accounts by a person resident in India) Regulations, 2000 - Notification No.FEMA 10 /2000-RB dated 3rd May 2000
7. Opening, holding and maintaining a Foreign Currency Account outside India :-
(6) A person resident in India who has gone abroad for studies or who is on a visit to a foreign country may open, hold and maintain a Foreign Currency Account with a bank outside India during his stay outside India, provided that on his return to India, the balance in the account is repatriated to India.
Thus you may get in touch with your authorised dealer to understand the documentation requirements for opening and transferring balances to such accounts.
As for taxability of such deputed personnel, please consider the provisions of the Indian Income-tax regarding residence status, provisions of section 192 of the Indian income-tax and the relevant provisions of the Indonesian tax act. This link may help you with the Indian side of things https://www.incometaxindia.gov.in/publications/2_TDS_On_Salaries/Chapter09.asp