Generally speaking, the deceased's estate is distributed in the following priority:
1. A surviving spouse or civil partner
2. Children and their descendants
3. Parents
4. Siblings
5. Siblings' descendants
6. Grandparents
7. Parents' siblings
8. Parents' siblings' descendants
https://www.goinglegal.co.uk/contesting-a-will/
Some of the most common grounds for contesting a Will in the UK are: Invalidity, Financial dependence, Fraud, Promised inheritance, Moral issues, Lost or destroyed Will, Laws of Intestacy, Unreceived inheritance, Mental incapacity and Third party beneficiaries. There are If you wish to contest a Will for a claim under the Inheritance Act, the time limit is 6 months. However, there is no time limit for contesting a will on the grounds of fraud.