I’ve been doing some research on this topic but it is quite a doozy…
Anyways this is a question for myself of course, and also for other fellow music producers with a similar question!
I wish to remix many songs of artists because I believe everyone is unique in their own way. In other words a song or track they produced is crystallized and cannot be duplicated or made better… it is unique to the person that created it. What I wish to do is promote myself and also the work of other artists such as Tupac Amaru Shakur and Nujabes… To keep their music more alive and to promote SOUL music not no mainstream bullshit! They are both great artists… also deceased. What am I to do? I don’t want to get sued for good intentions, I will always make bold claims as of where the original song/tracks came from. But I can’t ask them myself because they are in a better place now. I know Tupac didn’t make the instrumentals himself. Although Nujabes did and he is the founder of his own independent record label.
If anyone can give me any tip on what I can do to promote remixes of another artist’s music. I would gladly sign a contract to split the profit made but I know I can do better with the money I attain to help my fellow artists and the people of the world. Whomever reads this can take my words to the heart and mind and believe that I am legit and truthful or you can believe I am a money hungry individual… I am a man of my word the world will see that in due time so believe me now, never or later… it is irrelevant to my dreams and goals.
Thanks for taking the time to read this Y’all.
Both those artists had management and/or lawyers, and their estates no doubt have management and/or legal representation, you could approach them. Not sure how much success you’ll have, but its legal to ask! 
Tupac’s mother owns the legal rights to many of his albums. Nujabes was the founder of his own solo record label.
Any tips on how I can search up possible lawyers/managers? xP
Thanks again!