I have actually given this topic a fair bit of thought in the past. I was like you in that I had assets strewn about on various exchanges. I'll try not to give you advice, but instead tell you how I dealt with the problem.
There is a spot (in geography) that I can refer to in such a way that only my wife would know it's meaning. Also there is a deposit box, whose contents go to her in the will.
Finally, I have a Ledger hardware wallet that I used to collect all the coins and tokens from the various exchanges. I used the chrome extensions to gather the coins, and MEW with Nano for all the tokens. From there, I buried my nano's seed (along with instructions on how to retrieve funds) at the "spot", and then wrote my wife a letter informing of the existence of that seed at the "spot."
The advantage of this strategy is that if an unfriendly gets into the deposit box, then they cannot take the crypto, as they don't know the location of the seed.
I hope this helps somebody out there. There are too many instances of people dying without bequeathing their coins to their kin. Good luck with your perpetuation plan.
You might be right than if a stranger finds the deposit box before your wife they won't be able to access the funds, but that doesn't stop them from removing it from the safe location, and trying to get into it back at their property. So, this method isn't that foolproof as you likely wouldn't care if the package was missing, but you could verify that the coins hadn't removed, because the likelihood of the finding the deposit box would be unlikely at best.
So there's no real advantage if someone else finds it other than your wife, because the deposit box would likely still be taken, and beyond the reach of your wife just like it would be if they had got access, and taken the coins.
man, what can I say? Wow. I'm not sure if you understood what I was trying to say, but I know that I don't understand what you're saying. I don't know what you mean by "safe location" or what it is that "they" are removing from said location. I am confused.
To clarify, if I may, I don't think anybody will "find" the deposit box. This is not a scenario that I am guarding against. What I have here is a mechanism in place that protects against other (perhaps illegitimate) claims on the estate.