How can she save her deceased grandfather from the sin of consuming other people’s wealth?

Firstly: 

One of the most serious sins with which a person may meet his Lord on the Day of Resurrection is consuming people’s wealth unlawfully. It is one of the major sins that doom a person and make his burden of sins heavy on the Day of Resurrection, and it may lead him to Hell. We ask Allaah to keep us safe and sound. 

One of the gravest forms of wrongdoing and transgression is consuming the wealth of weak people such as women and orphans, whom Allaah has singled out for extra care and concern, and a sterner warning against consuming their wealth, because the wrongdoers find it easier to take their wealth because of their weak position. 

When Allaah mentioned the shares of inheritance in Soorat al-Nisa’, He also warned the one who transgresses against this shar’i division of wealth. Allaah says (interpretation of the meaning):   

“And whosoever disobeys Allaah and His Messenger (Muhammad صلى الله عليه وسلم), and transgresses His limits, He will cast him into the Fire, to abide therein; and he shall have a disgraceful torment”

[al-Nisa’ 4:14]

Allaah also listed consuming orphans’ wealth as a major sin. 

Allaah says (interpretation of the meaning): 

“And give unto orphans their property and do not exchange (your) bad things for (their) good ones; and devour not their substance (by adding it) to your substance. Surely, this is a great sin”

[al-Nisa’ 4:2]

And He says (interpretation of the meaning): 

“Verily, those who unjustly eat up the property of orphans, they eat up only fire into their bellies, and they will be burnt in the blazing Fire!”

[al-Nisa’ 4:10]

Usurping land is a major sin and the punishment for it is severe; the punishment becomes more severe if the land belonged to an orphan. The Prophet (peace and blessings of Allaah be upon him) said: “Whoever seizes a handspan of land unlawfully, he will be encircled by it down through seven earths on the Day of Resurrection.” Narrated by al-Bukhaari (3198) and Muslim (1610). 

It is strange indeed, by Allaah, to see someone who is keen to offer prayers and do naafil acts of worship, but then you find that he has fallen into sin by usurping people’s rights, and he has taken on burdens that mountains could not bear on the Day of Resurrection. His prayer, fasting and reading Qur’aan did not deter him from his greed and he did not show mercy towards the weakness of women, children and orphans, so he transgressed against the rights that Allaah has decreed for them, so after that how could we hope for him to be saved. 

Our sister, 

We ask Allaah to reward you greatly for your keenness to save your deceased grandfather from the punishment that you think is happening to him, but we can do no more than remind you of the reality that Allaah has stated in His Book, and that our Prophet (peace and blessings of Allaah be upon him) has stated, that usurping land and consuming people’s wealth unlawfully, and transgressing against the shares of inheritance, are all major sins, and if a man did not repent from them before he died (and repentance includes restoring people’s rights to them), if he did not repent then he is exposed to the punishment of Allaah. Then when the Day of Resurrection comes, those who had rights will take them from his hasanaat (good deeds) to an extent commensurate with their rights. If his hasanaat are all used up, then some of their sayi’aat (bad deeds) will be taken and added to his burden, then he will be thrown into the Fire, as the Prophet (peace and blessings of Allaah be upon him) told us in his hadeeth about the one who is bankrupt. Narrated by Muslim (2581). 

Your grandfather’s repentance from usurping the orphan’s land that you mentioned is not sufficient, rather he should have told him the truth of the matter and given him his rights in full. 

Al-Ghazaali (may Allaah have mercy on him) said concerning the conditions of repentance from transgressions against people: 

He has to tell (his victim) the extent of his wrongdoing before asking for forgiveness, because asking for forgiveness for something that the victim is unaware of is not sufficient. Perhaps if the victim realizes the extent of his transgression, he will not feel at ease with forgiving him and he will keep that until the Day of Resurrection and he will settle the score by taking from his hasanaat or giving him some of his sayi’aat. End quote. 

Ihya’ ‘Uloom al-Deen (4/47). 

Your grandfather has moved from the abode of action to the abode of requital, so you cannot do anything for him except two things: 

1 – Pray for him and ask that Allaah forgive him. 

2 – Restore people’s rights to them and ask them to forgive your grandfather. Restoring their rights to them – even if it does not excuse your grandfather completely – will undoubtedly reduce a great deal of the wrongdoing for which he is responsible. As you say that some of the people whose rights were taken have died, then you must give their rights to their heirs. 

Secondly: 

With regard to your paternal uncles, our advice to them is to hasten to return people’s rights to them. If they do not do that, then they will be usurping these rights, and they will meet Allaah with these major sins if they do not repent from them. Their saying that they “will never give their land to the people” is very strange, because they know that it is not their land or their father’s land. What they should say, which is in accordance with the truth, is “We will carry on usurping the people’s land”. We would think that neither they nor all the Muslims would knowingly expose themselves to the punishment of Allaah, for the punishment of Allaah is severe, and all the pleasures of this world are as nothing compared to a moment in the fire of Hell. We ask Allaah to keep us safe and sound.

We ask Allaah to help your uncles to repent sincerely.

And Allaah knows best.