So having a will, a death certificate, a solicitor, and willing to personally meet with Apple is now simple and convenient?
It has entered this thread quite late, but there is a big problem: If the old lady hadn't died, and had forgotten her Apple Id and password and went to the Apple Store, Apple wouldn't just reset the iPad. They would want some serious proof that it is really hers, and that she isn't trading in stolen iPads. That's the point of "Find my iDevice". Making it hard for crooks to access stolen iPads, which is unfortunate if the legal user forgets his password.
Now even with will, death certificate, and solicitors, the heirs can at most prove that they have the rights to the iPad that the mother used to have. But that might still mean no rights at all, if the iPad was stolen. They'd still have to proof that their mother was the legitimate owner in the first place.