RDJ's Sherlock is Tony's great grandfather. Howard's mother was related to the Holmes and it's through that they are related. Sherlock II (Benedict's) is changed a small bit. Stephen was adopted by the Strange family when his parents died, his father was Mycroft II. They'll watch RDJ's Sherlock movies being Tony's great grandfather and then Benedict's Sherlock TV series as Stephen's uncle. BBC Sherlock takes place more modernly, however, it is still before Stephen is born. Sherlock and Mycroft II are just that, the second. RDJ's Sherlock is the first while Benedict's is the second. I hope that explains it.