You can have the EPA drawn up, but you don't have to register it yet. That's when you inform relatons. The thing about informing the relations is that you have to inform at least 3, but this can include you. You work down this list in this order,
The donor's spouse,
The donor's children (including adopted children, but not step-children),
The donor's parents,
The donor's brothers and sisters (including half- brothers and sisters),
The widow or widower of a child of a donor,
The donor's grandchildren,
The children of the donor's brothers and sisters (i.e. nephews and nieces of whole blood),
The children of the donor's brothers and sisters (i.e. nephews and nieces of the half blood),
The donor's aunts and uncles (but not if they are only related by marriage),
The children of the donor's aunts and uncles (i.e. first cousins).
but you must include everyone in a particular category (if they are over 18)So if you have five siblings, you would have to tell all of them.
In the case of my MIL, when we register the EPA, as she has no husband, siblings or parents, DH & SIL will register it jointly, & that counts as 2. For the third, they will notify our DS who is 19, but not DD or SIL's children who are all under 18. But if they were 18, they would all have to be notified.