His brother, Mycroft.
Sherlock Holmes had one brother. His name was Mycroft Holmes. He was smarter than Sherlock, but did not like moving around the way Sherlock always did.
Sherlock Holmes's grandmother was the sister of the French painter, Vernet.
Towards the beginning of 'The Adventure of the Norwood Builder' we find this passage:
At the time of which I speak, Holmes had been back for some months, and I, at his request, had sold my practice and returned to share the old quarters in Baker Street. A young doctor, named Verner, had purchased my small Kensington practice, and given with astonishingly little demur the highest price that I ventured to ask - an incident which only explained itself some years later, when I found that Verner was a distant relation of Holmes', and that it was my friend who had really found the money.