Washington freed his own slaves (effective on his wife's death) but had no legal power to free slaves who belonged to his wife through inheritance. The two groups were intermarried and he didn't want to break up families so it was very difficult to come up with a solution--in a society where it was very difficult for a free black person to get anything other than the lowest-paying work. The whole legal system in Virginia was geared towards perpetuating slavery--it was only in the Revolutionary era that a mechanism was adopted to allow a slaveowner to free a slave.
Jefferson seems to have been conflicted--some of the strongest criticisms of slavery in that era are found in his writings, but he continued to hold slaves himself. He had a comfortable life at Monticello and could console himself with the notion that he treated his slaves well. Since he was deeply in debt I don't know if he could have legally given it all up and set all of his slaves free. If he could have it might have meant living the life of a poor dirt farmer--which is what the majority of his fellow-citizens were but that's not an easy change to make if you are used to a life of relative luxury. How many dirt farmers in Albemarle County drank imported wine?
It's easy to criticize him from this distance but we can't say how we would have acted if put in his situation.
One should remind some of those who get so sanctimonious in denouncing the condition of labor--particularly agricultural labor--in other times, in any region; that the Patriarchs in the Bible employed a similar labor system. Abraham & Isaac were not paying wages to those dependent upon them for protection in a managed economy. And there is no mystery why Jesus did not denounce slavery in a later era.
To paraphrase American Indian wisdom: "You should not criticize a man, until you have walked seven miles in his moccasins."
William Flax