A solicitor will need to be satisfied that your loved one understands who will receive what and that they aren’t being pushed into making or changing their will. In essence, it needs to be clear that your loved one is making their will independently.
While they don’t have to use a solicitor, it's recommended that they use one, especially given their dementia diagnosis.
Your loved one doesn’t have to legally seek a medical opinion or involve their GP when they make a will. However, for an older person or someone with a condition affecting their ability to make decisions, they should ask their GP to certify that they have what is known as ‘testamentary capacity’. This is to protect against someone challenging the will in future and claiming that your loved one lacked capacity when it was made.
If your loved one lacks capacity to make a will, it’s recommended that you seek advice from a legal professional. You may need to seek deputyship to protect their interests. A deputy is a person appointed by the courts to manage the affairs of a person who lacks capacity. A doctor usually completes an assessment for the person and the person’s details, including information about their assets, must be sent to the Court of Protection.
A deputyship can take four to six months to complete, but this can vary depending on individual circumstances. The Deputyship order needs to be authorised by the court.
As you can tell, this can be a lengthy process, so if you feel the person still has capacity to make a will, they should do it as soon as possible.
Sources:
https://cunningtons.co.uk/services/wills-probate/deputyships/