There are certain requirements that a will must comply with to be a valid will. Any person can of course attack the validity of the will and take the matter to court. There is the case of the 4 brothers who had a very wealthy father who owned several farms, cars and properties.
The father left a will, but for some reason he left a will that had, according to the sons, an unfair effect. Two sons were left with 2 farms each and the other two sons were left with cars and some cash. The two sons who inherited the cars and cash were very upset and took the matter to court, to say that the will is invalid. Well, the four brothers fought for years in court and ….everybody ended up with nothing because the legal expenses were so high that they had to sell t heir assets to pay for the legal costs.
In the end the court found that the will was very valid, despite the unfair (according to the two sons) effect it may have. By then it was too late as all the brothers ended up with nothing. And never spoke to each other again.
Sometimes it not the wisest thing to do to fight the validity of the will just because it is unfair.