AITA for asking for my dead friend's Pokemon collection?

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The original was posted on /r/AmItheAsshole by /u/anon_pokedude on 2023-06-27 03:37:03+00:00.

My friend ("Jack") tragically passed away 6 months ago and his mother ("Lisa") invited me over recently as she was cleaning out his room. There was a collection/binder of Pokemon cards that she had planned on throwing out but I convinced her to instead give it to me.

Fast forward a month later and Jack's sister ("Elly") is angry at me for taking the Pokemon cards, despite her having no interest in Pokemon and having had 'first dibs' at my friend's old stuff. She's demanding I return the Pokemon cards, because she wants to sell them, so she can "use the money" to help out Lisa.

I feel torn because I had double checked with Lisa that Elly didn't want the cards and she assured me that I shouldn't worry. I've told Elly that as Jack was my best friend and that I double checked with Lisa I am going to hold on to the cards.

AITA?