You only pay one fee for the whole exchange between us.
It is the wording of the will which is important.
If it says words such as “I leave everything to my children” it includes illegitimate children and adopted children. It also includes any children who were born at the time of writing the will.
Not being named on the birth certificate is not relevant. The age of the child is irrelevant.
If it says words such as “I leave everything to my children Fred and Tom”, then all the children are excluded.
Another child may have a claim under the Inheritance (Provision for Family and Dependents) Act which would have to be brought by a parent or other interested party as a Litigation Friend because a nine-year-old is not capable of conducting legal proceedings.
If you are the executor, they cannot take over anything. You are appointed in the will and provided you go along with the wishes in the will, you cannot be criticised. If they are now harassing you over this, call the police because they either have to go to see solicitors and deal with it legally through the courts or leave you alone.
It is worth saying that if this was taken to court on behalf of the nine-year-old child, the nine-year-old child is likely to get something under the Inheritance Act because the father has failed to make adequate provisions for that child. Further, it’s likely to cost quite a lot of money in legal proceedings if it’s defended. It would be in the other 2 beneficiaries best interest to come to an arrangement with the grandparents acting on behalf of nine-year-old whereby the nine-year-old gets something. You are not able to take that decision because the money has been left to the other two children. That decision must be taken by them. My advice to them would be to really consider splitting it three ways and certainly don’t try to defend any claim under the Inheritance Act.