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if i am to believe how nlocktime works (sorry havent looked deep into it), but by going by your description the tx wont be mined until it reaches a certain blockheight.
this means that the tx just fills up the mempool of miners and nodes waiting for the right blockheight to then finally be mined..
with that said writing this tx on a piece of paper in your legal Will is meaningless..
afterall whats it preventing? you dont know when you are going to die, you dont know if the intended recipient will know what to do with the funds received when this psychically predicted death time passes..
you might aswell just sign a standard tx and write that encrypted tx data into a will with instructions on how to push it..
as for your set up seeds.. if you write the seeds in your legal Will, nothing is there to stop the lawyer from reading it and draining it of funds because they have the private keys to send it wherever they want..
however, only writing a signed tx where the destinations are already encrypted into the TX in a legal Will means no one knows the privkey/seed of the originating fnds. no one can change the destination. and thus the only thing that can happen is the tx is pushed, where the intended recipients get the funds.. or its not pushed and the funds remain untouched because no one knows the privkey of the originating funds to tamper or move elsewhere.
which at the reading of the legal Will.. where you would have lets say 3 recipients. there are in total (including the lawyer) 4 people that would have motivation to push the tx.
so knowing your own privkey wont be spread about and abused by greedy people, your at ease, and now you can the give out the other privkeys(of the receiving addresses, not the origin funds) to the intended recipients right away and tell them to keep hold of it as inheritance.
because ofcourse them only having the receiver addresses is meaningless while your alive.. there is no funds in them and the privkeys are nothing to do with your own address that has the funds. it also means the lawyer wont ever see any privkeys, either because you only handed a signed tx to the lawyer and because you handed the recipient privkeys direct to the inheritors, and not via the lawyer.
in short
just write a signed tx in your will.. and hand the recipient addresses to the recipients. then you dont have to worry about anyone else messing with the funds because they wont have the privkeys to the original funds