But there our warranty stops.

We can deal during our trusteeship with the corpus only.
Further, lest there should arise any error on your part, we can deal with any general instruction for only so long as it may remain unrevoked.

You are, and must be, free to alter your instructions or authorizations at any time.

Thus your latest document must be used for our guidance.
As to the general principle involved in your wish I make no comment.
You are at liberty to deal with your own how you will.

I quite understand that your impulse is a generous one, and I fully believe that it is in consonance with what had always been the wishes of my sister.