One way to think about how many of Massachusetts' "patriot" leaders were enslavers is to imagine a dinner party John Adams attended in Boston in 1771. Of the ten men at the table, eight were enslavers, and they talked about other enslavers.

@MHS1791
https://www.masshist.org/digitaladams/archive/doc?id=D17&bc=%2Fdigitaladams%2Farchive%2Fbrowse%2Fdiaries_by_date.php

One of the topics of conversation was a garish candelabra recently given to Harvard by Dr. John Cummings of Concord. The party mocked the gift for its bad Latin and for its pretension — Cummings was a try-hard country enslaver trying to be like Isaac Royall.

Isaac Royall owned a sugar plantation in Antigua and enslaved hundreds of people there, along with dozens more at his home in Massachusetts. He gave the gift that founded Harvard Law School. https://royallhouse.org/ 

The host of the party was Capt. John Bradford, a member of the Boston Committee of Correspondence. He enslaved several people, including Chloe Spear, who may have cooked the food for the meal.

The Memoir of Mrs. Chloe Spear was published in 1815.

https://docsouth.unc.edu/neh/brownrw/summary.html

One of the guests was Rev. Samuel Cooper, minister of the Brattle Street Church and a member of the Harvard corporation. The party discussed at length a parable related by Glasgow, a man enslaved by Cooper.

Another guest was Cooper's brother, William, the Boston Town Clerk. He enslaved Betty Cooper. Don't let anyone tell you that the Founding Fathers didn't know any Black trans women. Betty Cooper's enslavers called her by a male name, but she was "well known" as Betty Cooper.

Another guest was Rev. John Lathrop, pastor of Boston's Second Church. His wife was Mary Wheatley Lathrop, whose family enslaved the poet Phillis Wheatley.

Another guest was Dr. Joseph Warren, who "purchas’d a Negro Boy of Joshua Green" on June 28, 1770. He paid £30 up front and promised to pay a further £10, “to be paid in Potter’s Ware manufactur’d in this Town."

@MHS1791
https://www.masshist.org/database/564?mode=transcript

Another guest was Thomas Brattle, a wealthy merchant and enslaver. When Dinah, a woman he enslaved, died in 1798, newspapers reported that she was 100 years old.

Another guest was William Greenleaf, future sheriff of Suffolk County, whose tax records show that he enslaved one "Servant for Life" in 1771.

http://sites.fas.harvard.edu/~hsb41/masstax/masstax.cgi

Another guest was "Dr. Greenleaf," who could have been either of William's brothers, John or Daniel. If it was John, he previously enslaved a teenage girl named Phillis who was executed at age 17 for allegedly poisoning Greenleaf's children. https://twitter.com/cgdhopkins/status/970678318465998848?s=20

The other two guests, John Adams and James Otis, did not enslave anyone as far as I am aware.