Sorry to hear the sorry state of affairs at your end.
You can first send a legal notice to your NRI Son and daughter-in-law that they sop forcing you out of your own house post which you will have to take criminal action and also file a civil suit for eviction. That should be sufficient.
For further queries, you can contact me on 7601090381.
you can reclaim your flat by ousting your son and daughter in law by court order. You can contact me to file a case of eviction against them after serving a legal notice upon them. 9013429126 is my contact number.