WOW!

My oldest sister lives closest to our parents and her name is on all of their accounts. It has never once crossed my mind that I or our other sister should be on those accounts.
The 3 of us are extremely close though and trust each other explicitly when it comes to handling our parents affairs. And even if my oldest sister were to "keep" whatever accounts her name was on--it wouldn't bother me as she's the one who has actually been the one to take care of Mom & Dad since she's the closest.

I guess what I'm getting at is: A) I don't understand the misgivings of your DH and the other sister about the situation, 2) it does look like what they care about is the money, 3) life is short---do you really want to waste any of the time squabbling over who's on what account?

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Mental that one, I'm telling you. ---Ron Weasley, "Harry Potter and the Chamber of Secrets"