13 years

Thirteen years ago, Sherlock and John had decided that, now that they were married, it was time to get a child. They got three siblings. The eldest, a raven haired girl with tan skin. The two younger ones were twin boys, one with curly raven hair, matching his sister, and the other with curly blonde hair, matching one of his dead parents.
But of course, Uncle Moriarty will never be please with their happiness.