You can file a police complaint for cheating and  fraud though the burden of proof is on you.

Further since the will is already probated the same has to be challanged along with cancellation if the transfer of property.

File police complaint of cheating, fabrication of documents,forgery against the 4 sons 

2) also take out application under section 263 of Indian succession act for setting aside probate granted by high court on grounds of material suppression of facts 

3) 

Section 263. Revocation or annulment for just cause.--

The grant of probate or letters of administration may be revoked or annulled for just cause.

Explanation.-- Just cause shall be deemed to exist where--

(a) the proceedings to obtain the grant were defective in substance; or

(b) the grant was obtained fraudulently by making a false suggestion, or suggestion, or by concealing from the Court something material to the case; or

(c) the grant was obtained by means of an untrue allegation of a fact essential in point of law to justify the grant, though such allegation was made in ignorance or inadvertently; or

(d) the grant has become useless and inoperative through circumstances; or

(e) the person to whom the grant was made has wilfully and without reasonable cause omitted to exhibit an inventory or account in accordance with the provisions of Chapter VII of this Part, or has exhibited under that Chapter an inventory or account which is untrue in a material respect.

Hi,

Out of many other sections of Cr PC you may add section 340 of Cr PC for perjury if will is probated in court.

After probate is granted to executor of the will can not be said to be a fraudulent will. 

However you can challenge the will again after probate if you can establish the fact that will was made fraudulently, with proper evidence.

So at this stage no criminal case can be filed.

But you can challenge the will. 

1.Yes for forging a Will criminals case does lie for which you can lodge complaint in police station on which basis FIR can be registered.

2. Since citation was done while getting Probate of the Will, this a valid ground for challenging the Will and hence file an application for revocation of the grant of Probate.

3. Considering the proof you have the grant of Probate would be revoked for sure.

4. This is essential to challenge the Will since your daughter has share in the property which would have been inherited by her mother.

So seek justice for your daughter.

Sir,

     You can file fir against 4 sons in the police station for cheating, forged documents, facts hide from the court.

     Challenge probate of the will in court.

     For this appoint a local lawyer.

When mother in law expired and what is the date of execution of WILL ?

you can file police complaint u/s 420 468  of ipc against them. 

Yes you can lodge FIR against the brother of your wife for making forged documents and cheating for transfer of property to their name. 

Its difficult on limitation ground but you can a private complaint if FIR is not recorded

You can challenge the Will in court of law in case they are relying upon the Will to grab the property fraudulently as observed by you.

Or else you may file a partition suit claimning yo deceased wife's share in the proeprty ignoring the existence of Will stating the owner of the property died intestate hence your deceased wife has a share in the property as one of the legal heirs to deceased property owner.

Let them produce the Will before court which can be challenged for its genuineness during trial proceedings.