Doyle does not draw on ANY of the characters not just Mrs Hudson and Mrs Watson. We are given NO details as to Holmes' private life and scant details about Watson's.
Doyle didn't include it because he didn't feel it was relevant.
In a Scandal in Bohemia Watson talks of his marriage, how happy it has made him and how he saw little of his "former friend". Note the word "former" here.
Holmes is described by Watson thus: "all emotions, and that one [love] particularly, were abhorrent to his cold, precise, but admirably balanced mind....as a lover, he would have placed himself in a false position....for the trained reasoner to admit such intrusions into his own delicate and finely adjusted temperament was to introduce a distracting factor which might throw a doubt upon all his mental results."
Please try to understand my point.
It is not that they have modernised Holmes, nor built on other characters or even that they have introduced new elements to the stories, but that they have changed the fundamental personality of Holmes.
They got him drunk. Holmes would never have allowed his mind to become so unfocused, he was a man who remained in control AT ALL TIMES.
They had him give a speech at a wedding with 'hilarious' results. Yet Holmes "loathed every form of society with his whole Bohemian soul."
They have made him appear vulnerable, even fragile.
They have made him out to be self analytical when in truth, he couldn't give a toss what people thought of him and would never have spent much time wondering why he was so different.
They made him foolish. Yet Holmes was rarely wrong, he never acted spontaneously but with careful and deliberate thought. Nothing would have escaped his attention and those who sought to fool him with clever disguises were always revealed by him within seconds.
They have turned him into a murderer. Holmes may have pistol-whipped people and he was a fine boxer who could certainly defend himself but to shoot someone? Watson was in no danger - Holmes would not have shot anyone.
Yes he cared about Holmes, that is apparent in the stories.
He was not dismissive to women at all. He kept the photo of Irene Adler - the first person to ever outwit Holmes (thank you Doyle) but there was also Violet Hunter in the Copper Beeches whom Holmes admired so much that Watson thought he might stay in contact with her.
There were many men who Doyle made just as foolish and in fact Holmes agreed with the King of Bohemia that Irene Adler was in a different league altogether from him, and he didn't mean it as a compliment to the King.
Doyle wrote for a Victorian audience and I think, under the restrictions of the age, he did very well.
My main objection to BBC's Sherlock is the unravelling of the character himself. If you take away the mystery you take away the appeal. Holmes is not meant to be understood and analysed and pigeon holed.
He's been labelled a sociopath (not true), he's made out to have suffered as a victim of bullying, his nature revealed because of a traumatic childhood, his parents wheeled out, his vulnerabilities exposed, etc.
That he would ever have agreed to go on a stag night, that he would not notice Watson spiking his drink, that he would allow himself to get out of control, that he would not notice Mary's deception, that he'd allow people into his private life (he and Watson were long time friends before Watson even found out he had a brother) that he'd psycho-analyse himself, that he'd shoot a man in cold blood (not even in defence and kill someone who was not even a murderer) none of these things ring true.
They've just stamped all over the character of Holmes. By all means modernise the stories and add new elements, new characters, new thrills but don't take away the one constant feature which is of the Great Man himself. Not unless you are doing an obvious parady, which they deny.
As for family affairs - Moffat and Gatiss said that they chose BC's parents for the resemblance. They must have adopted Mycroft then.