You need to check any GR has been passed away from State Government for that particular survey number which got transferred into natham. .... You can find all details on government website or in collector office or you can ask sub-registrar GR details.

You need to apply village administative officer or agent for the same. Once the application is processes and payment is made then it's converted

Well.  The change of nature of the land doesn't make much relevance as long as name of the Pattqdae remains same. 

Now since your grandmother has died and if she has not left any Will then all her sons and daughters would be entitled to mutate their names.

So first do so and then try to change the type of land.

On grandmother demise property would devolve on her legal heirs ie her children 

2) Grama Natham’ means village house site. The same can be used for residential purposes and can also be freely transferred from one person to another. The restriction is that the same can be used only for a single dwelling unit and the land cannot be exploited commercially i.e., cannot be used for construction of flats

3) file RTI application as to on what basis dry  land is being shown as Natham Land 

You can at Tamil Nadu Government website that your survey number show natham or not. Kindly provide the survey number let me check in details.

Serve them with a legal notice and than file a specific performance suit against them for conversion 

The procedure is as stated above only. You need to submit necessary documents and do the same

File RTI application as to how your  dry land has be classified  as Natham land after so many years of ownership 

Please apply for certified true copy of all survey no of all patta. We will come to know who is liar records or Dy Tehsildar.

Challenge the said decision before the Land Tribunal or the High Court as stated above. 

1. You can apply to the district collector office for a hearing and request to restore the land to its original status.  Do this thru a local property lawyer.

You may seek how the patta land was converted as a natham land by an RTI application addressed to the revenue authority concerned. Upon obtaining all relevant information, you may consider appropriate further action.

Once the Dy. Tehsildar is agreed to transfer the patta to your mother's name what problem do you face now?

You can go ahead. 

Are they insisting on the particular survey number alone and not cooperating with you. 

Then you first issue a legal notice demanding them to transfer the patta of the land whose survey number was  reportedly converted to natham. 

Let them give a detailed reply with rules in this regard. 

After that you can file a suit for declaration of title deed on your name and for direction to concerned revenue department to transfer the patta to your name. 

- As per law, Patta is a type of land deed issued by the government to an approved cultivator with a land revenue exemption.

Since the said property is in the name of grand mothers for more than 100 years, hence legally you can change the same in your mothers name , after releasing respective share in her name, as after the death of grandmother her property can be claimed by her legal heirs. 

-  Further, Grama Natham land can only be used for residential purposes and not commercial. 

- You can file an RTI application to know the same. 

We suggest you should consult a local civil lawyer who can examine facts of the case based on the documents and facts.

You can make an application under RTI to find out the reason and time on which the land was changed to Natham land.

After getting reply you can file suit to claim compensation for changing patta land without consent or claim rights of land back to your name.