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.