Non payment of salary since last 16 months.

My father worked as a supervisor in a I.T.D.C ( Indian tourism development Corporation, A government enterprises) affiliated hotel from last 32 years and are on the verge of retirement in next 2 years. Unit under which my father was working has only 4 permanent employee ( these employees are also at the age of retirement) rest are on contractual basis, this unit was doing good business as compared to other units run by i.t.d.c. In March 2017 this unit was included in sick company list and was handed over to R.T.D.C ( Rajasthan tourism development Corporation) with a M.O.U signed between ITDC, RTDC & employees of this unit, stating that these 4 employees will be handed over to RTDC on deputation for the remaining years of their service with same salary, designation and other official benefits. But, since March 17 to till date, none of these employees have received the salary. They are working without salary from last 16 months. Once a compensation of RS 2lacs was given. But rest of the salary is not yet credited and now telling that they cannot keep them with same salary and designation and offering 3 grades lower salary and designation. Since then we have already written to RTDC, itdc, PMO and to ministry of tourism at State and center. But no reply has been received. Now we have decided to file a suit against them. Kindly suggest how to proceed.