First of all my condolences to you and your family.
Instructions as to how to obtain an NIE number, plus instructions on how to fill it in, can be found here:
However I would check with a lawyer whether you need an NIE number in this case.
I’m not sure what you mean by “la 8a ye” but I guess you are referring to the Hague convention Apostille (La Haye in French). You can get this from a British Notary.