Hemings family
Thomas Jefferson wrote a lot, so historians know more about the Hemingses who lived on Monticello than about many other enslaved people.  We know that six of Elizabeth Hemings' children were Martha Jefferson's half-brothers and half-sisters because they had the same father: John Wayles.  We do not know what Martha Jefferson or the Hemingses thought about this.  We do know that Robert and James Hemings helped Martha Jefferson and her daughters escape from British soldiers during the Revolutionary War.  We do not know whether the Hemings men thought of themselves as two men helping their sister and nieces, as two men helping their master's wife and daughters, as both, or as neither one.