In order for a will to be legally valid, it has to be witnessed and signed by two independent adults. They are there to check that the will writer knows what's happening and isn't being pressured into signing. A witness must be over 18 years old. They can't be: Related to the will writer A beneficiary of the will Married or in a partnership with any beneficiaries Most people choose neighbours, friends or colleagues as their witness. You can also choose a professional such as a solicitor or GP.