A woman got married to a man who is older than her by 20 years. He did not inform her about infertility problems he had before marriage. She assisted him in buying a home in a European country, where they live. She recently found a will he wrote before admission to hospital for prostate operation. He is giving land he owns to his sister, pension payments to his brother, half of their home to his wife (as that is the law of the country), quarter of the home to his mother, quarter of the home to his wife (as her part of the well).Is it a fair distribution of will in Islam? The woman is aged 44 years and she has been sympathying with his health problem during the past 12 years.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

In Islam, inheritors have rights according to the Sharee'ah. So if a person writes a will specifying the details of the inheritance, then this will is invalid unless all inheritors agree with it. The Prophet said: “There is no will for an inheritor.” [Ahmad and At-Tirmithi who said that it is a Hasan Hadeeth]

Imam Ibn Abdul Barr said: “All Muslim scholars have agreed upon this ruling.”
Therefore, the will mentioned in the question is not valid as long as it includes something that is not in accordance with the Sharee'ah.

Now there are two choices:

a) The inheritance should be distributed among all inheritors according to the Sharee'ah.

b) If all the inheritors agree with the will, it will become valid.

For more benefit that there is no will for an heir, please refer to Fataawa 26630, 289471, 302158, 312970, 317632, 336970, and 350614.

Allah knows best.