From what I have read Washington specified that his slaves should be freed after his wife passed away. However, she ended up freeing them promptly after his death. I guess because they had a vested interest at her death, and she didn’t want to be looking over her shoulder.
Martha was a wealthy widow when Washington married her, it was she who probably owned the slaves that worked Mt Vernon
Interesting how many of our enlightened Founders who were born into times when slavery was a way of life, freed their slaves