D son cannot sell the property as he has no right , title interest in the property 

2) he can file suit claiming ownership of property on basis of adverse possession.that he has been in open ,hostile , uninterrupted possession for over 12 years .The Supreme Court has said that a suit for declaration based on adverse possession which has matured into ownership would be maintainable.

3) A Person who claims adverse possession should show: (a) On what date he came into possession, (b) What was the nature of his possession, (c) Whether the factum of possession was known to the other party. (d) How long his possession has continued, and (e) His possession was open and undisturbed.

1. Limitation for probating will is three years from the date of challenge to the  will, as will is not challenged yet, it is within limitation.
2. Claim of adverse possession is not available against true owner of property even possession is more than 100 years.
3. Your best option is to challenge the self acquisition of property by grandfather. There are many in which it can be proved as ancestral and get the  will invalidated.

D's Son has to approach the jurisdictional Civil Court and pray the Hon'ble Judge for declaring him as the Owner of the property, based on Adverse Possession for more than 12 years, without objection for his possession from no one, since 24 years.

- Since the said property was purchased by your grandfather , then he was having his right to transfer the same to anyone including A & B without taking the consent of C or D after writing a WILL in their favor. 

1. As per law , probate is not mandatory and it is needed when there is dispute amongst legal heirs. 

2. Since the property is in possession of D , then he can claim ownership on the ground of adverse possession. 

- His son can file a declaration suit before the court for declaring himself as the owner of the property. 

Presuming there is no probate of Will and also the A and B has not taken any action to transfer the properties to their name, if it is treated as intestate properties then along A and B, the C and D are also having equal shares in the properties.

Therefore D's son cannot sell the property in entirety by himself, he  cannot sell the property during the lifetime of his father.

D's possession of property is illegal and he has to vacate and deliver possession to the legal heirs of the grandfather once they decide to partition the property ignoring the Will or if A & B decide to enforce the bequest made through Will, they can act on the Will by submitting an application to the revenue department to transfer the property to their names in the revenue records.

D's son, if not willing to vacate the property, he can be ejected from the property through a civil suit for ejectment. 

D has taken possession of the proeprty illegally especially when he had no rights or interests in the property, hence he can be made liable for criminal offence  under the provisions of anti land grabbing act also. 

Mutation of property has not been done as per will 

will has not been acted upon 

it would be difficult for D son to sell the property 

Your understanding is right.

D has no rights in the property especially during the lifetime of his father.

Besides his father is not a beneficiary of the Will. 

Therefore the beneficiaries of the Will can claim the rights over the property and can get the revenue records  duly transferred to their names by submitting an application before the concerned Revenue department, of course they may be asked to produce the NOC from other legal heirs of the deceased testator or to produce probate order from court.  

1. The property dis not belong to D for which his son can not sell the said property.

2. D's son can claim adverse possession once A & B claims the said property but it will be difficult to get adverse possession of the said property against the blood related owners.

1. The property has been bequeathed to A & B by virtue of the Will for which the question of D's being the legal heir does not arise in the instant case.

2. A & B can now file an application seeking probate of the Will to claim title of the entire property.

Law of limitation is not applicable to ancestral property. There is no such limit of 12 yrs to claim ancestral property. 

If he had knowledge and he didn't challenge then the limitation has ceased

Now its time barred matter

Dear client,  I am sorry to hear that but in this case the property was a self acquired property therefore your grandfather can will it to anybody he wants and nobody can claim that right on the property. Therefore the son will have no right over the property until and unless the whole will guest challenge before the court.

- The WILL can be challenged on the ground of late information of the Will , and if the said Will not performed by the beneficiary. 

- Further, this limitation period is not applied in case of an ancestral property .