Yes you can file FIR against him and contest the case you will get justice

Since it is grand father self acquired property he has no right over it file.a suit for permanent injunction against him , he cannot claim any right In it also his sign is not necessary for same.

Also ask police to register FIR and proceed against him.

If you are absolute owner and property is registered on your name then you can file a suit for declaration and permanent injunction. 

Record his threats 

2) since FIR has been lodged police would conduct investigations and file charge sheet 

3) file declaratory suit that you are absolute owner of lan d as per deed of family settlement signed by all parties 

4) I presume deed of settlement is duly stamped and registered 

Go for a partition suit or get the property partition by metes and bounds by appointing arbitrator. You can develop construction on land of all other except on the share of land to the opposing party.  If the land of the opposing party is necessary for construction, then only way is to make him agree for relinquishing his share for consideration. A good amount  of consideration may serve the purpose.

File Civil suit and get injunction order order agasint him, still he violates court order or creates disturbance court will send him in jail.

Dear Sir,

You may approach civil court and get injunction order restraining him and his supporters from interfering with on going constructions.  Such share is legally given to you as such he cannot make any issue out of it.  Approach High Court and get stay order on the FIR lodged by him.

1) un registered agreement for division of property   By metes and bounds woukd be in admissible in evidence 

2) obtain court orders restraining uncle son from disturbing you carrying on construction 

3) file suit for partition for division of property by metes and bounds 

4) file FIR under section 504, 506 of IPC 

If this property in which you are constructing a structure has been allotted as your father's share and you people have been enjoying the same ever since the allotment, then you may file a permanent injunction suit against them restraining them from interfering in your possession and enjoyment.

If the local police are not effective you may approach the district top police officer and submit an application narrating the entire episodes and your pathetic condition while requesting him to intervene and direct the local police  to give protection to you and also to initiate proper legal action against the culprits.

 The notarised agreement is not valid in law and cannot be enforced in law, hence a partition suit before the court would solve the issue.

Police cannot stop the construction, you may appraoch the higher police officer against the local police seeking protection and proper action on this.

As the property has not been properly partitioned and the issues have not been properly settled among the shareholders, it would be advisable to stop the construction for the present and approach court with a partition suit for remedy to this.

You can appraoch civil court seeking injunction.

You can file a counter complaint against them for their atrocious acts 

You need to take court orders for construction no one will disturb you. Counter FIR will depend what charges they file in their FIR. The unregistered agreement may turn weak before court but still will have some weightage.

1. See if grandfather made settlement and partition in his life it is valid.

2. Police cannot stop construction he needs court order,

3. See the land has to be divided among all beneficiaries and then on same in your portion you can construct.

4.See without any legal step from him we cannot assume what step he will take you can register a case against him police and can start constructing. 

5. See injunction order keeps him away from property still he can file case for same.

6. See your mother can put a case of harassment , violence and intimidation against her if he do so.

Family settlement requires registration. Police has no role in such matters, get injunction order from court. On the basis of possession,  You can construct or file partition suit so that court will partition equally .

Court will grant interim injunction on first hearing than case can go any longer. FIR not maintainable but for any physical violence or assault can file FIR.

No it is not. 

If he gets any stay from court then only the work can be stopped else no one can stop it. 

You can take permission if required

if there is no stay order passed you are at liberty to carry on internal work 

you must have building sanctioned plans ,you can carry on construction of no stay order has been passed 

1.  If he has slapped notice just ignore it and proceed with your construction work till you are not restricted by an order of court to stop the activities.

2. If you have been stopped to construct by an injunction order, then you may file a petition under order 39 rule 4 cpc seeking to vcate the injunction order and also may file a petition seeking permission to construct the same, now you have not been restricted hence you may continue the work,

Notice sent by him or lawyer is not binding, and you are free to continue.

If Court notice, still it dose not meant stay and can continue.

1. See if any order or stay on construction is there then it would be contempt.

2. See if no stay then you can carry on with work and can reply there application.