My uncle married his wife for 15 years got one son and one daughter

His wife mother got 2 properties:
1) wife share with mother 50/50. Mother help pay down payment 100k for 500k property. But the wife work her ass off to pay for property (most of her salary go to the property). As a result, uncle have to tanggung most of the household expenses for 15 years. He feel like he is indirectly paying for the property in which the wife mother has 50% share. The mother has said that she will pass the 500k property to his wife. But she pay most of it.

2) Bangalow worth 3 mil where mother and brother is living there. Wife mother decided to pass the whole Bangalow to the brother who was single.

Issue: my uncle has 2 kids (my cousins) and he feel it is unfair that they lost their inheritance. They inherit a property that is mostly paid by his wife as mother only help 100k downpayment. My uncle not interested in the Bangalow, he only want his kids to benefit. Wife decided not to contest and give to the brother everything. But recently the brother found love and is about to be engaged.

Issue2: my uncle has good relations with his mother in law n brother. But his constant persuasion with his wife on this matter would threaten to make relations worse as this is a sensitive matter.

Issue3: my uncle feel unfair he has to work hard and sweat while the wife unable to contribute due to the mother persuasion to make her buy this property when he was bf and gf with her.

Issue4: my uncle not interested in the Bangalow but he wants their kids to have a share for their future

Conclusion: if you were in his shoes, what would you do?
1) leave it as relations with in laws more important
2) fight for children all the way
3) do it diplomatically but wife still not listen then forget it