Dear Mycroft,
I see that your diet hasn't been going so well, as you appear to have put on half a stone in the last month. Perhaps a visit to your brother would be beneficial in this case. You always did have a tendency to overeat when you were worried, and your concern over your brother's living situation has apparently become rather detrimental to your health.
I understand that travel generally doesn't agree with you as it completely disrupts your routine but, an exception should be made in this case if only to confirm that your concerns over your brother's welfare are as well founded as you suspect. We both know full well that the Americans aren't as civilized as we, and life in New York contains more potential hazards to your brother's health and safety than London does.
The change in environment may prove to be what your brother needs at this time however, as certain temptations have been eliminated by their distance from your brother's current location. That, and it would significantly cut down on the number of arguments between the boys that have inevitably arisen due to my brother's territorial nature. It is quite fortunate that my brother is significantly fonder of DI Lestrade than he is of Gregson, otherwise there might have been a murder following Gregson's departure. As you may remember, things came close enough to ending that way following the dumpster incident.
I believe your concerns over your brother's new companion are unfounded despite the fact that your father hired her. Your brother appears to be settling in with Ms. Watson in much the same way that my brother settled in with his flatmate. Should things progress as I believe they will, the former doctor will prove to be the perfect foil to Holmes. With someone to bounce ideas off of and use as a sounding board, your brother should reach greater heights than he would have alone. That, and if he has someone to keep him occupied, his desire to resort to illicit substances in order to stave off the boredom that inevitably results from inactivity should be substantially reduced much as it has been for my own brother.
Now that I think about it, you should have your brother bring his companion to the next family reunion. The added confusion should prove entertaining and, as you know, we will need something to stave off boredom during the event since both Sherlocks have been forbidden from coming within fifty feet of any fireworks during any family gathering.
As always, I remain
Your Cousin,
Mycroft Holmes