At one point in Rainbow Rowell’s Eleanor & Park, Park thinks:
He loved how much they loved each other. It was the thing he thought about when he woke up scared in the middle of the night. Not that they loved him—they were his parents, they had to love him. That they loved each other. They didn’t have to do that.
And I think that Hamish Watson-Homes would think of exactly the same thing. Sherlock will snog John when he comes home from the surgery, and Hamish will wake up to the sound of Sherlock’s violin and the knowledge that his parents’ love is… miraculous.