Multiply (the sum of our parts)

After Reichenbach and in order to 1) Keep Sherlock alive, 2) Keep John alive and 3) Get Sherlock home to England as soon as possible, Mycroft devises a plan that will not only incentivise John's continued sanity and survival but force Sherlock to come running. It is a perfect plan, though perhaps less than ethically sound. He has no doubts that using frozen samples of your younger brother's sperm to create children for his husband to care for falls deeply within the realm of socially unacceptable behaviour, but it is efficient, and that is what matters most.