Hamish Alexander and children
Emily and Hamish could, indeed, have had children. They had not done so prior to Emily's accident because they were both prolong recipients and figured they would have "plenty of time" once the ruinous temporary (of course) time demands of Hamish's naval career during the early buildup against Haven had relented somewhat.
They have not had children since the accident because Emily has chosen not to. Her reason is that it was not until her accident that she became aware of certain problems in her genotype. Specifically, the reasons she does not regenerate. Honor's problem is that her engineered genotype is "locked," and aspects of the tinkering which was done to create her heavy-grav tolerance inhibit regeneration in about 40% of the people who have it. In her children, a little genetic modification (which can be easily accomplished after conception) would permit that inhibition to be removed. In Emily's case, the genetic problems which peclude regeneration are much more complex and cannot be corrected without risking the introduction of several other dangerous disease states. Moreover, the odds of repeating the problem in her case is almost 3-in-1.
Given her own experiences with the consequence of being unable to regenerate, she has chosen not to have children of her own who would be likely to share the same problem. (No one ever said that paranoia had to be logical, and given her life experience, she is downright fanatical about not exposing another child to it.) Willie Alexander is married (you should meet his wife in the next Honor novel) and has several children, for whom Emily is the doting aunt and who secure the Alexander succession, and she and Hamish never really "needed" children to confirm their love for one another. Now, if it should just happen somehow that Honor and Hamish were to somehow end up reproducing (not saying it's gonna happen, y'unnerstan', but if it just happened to), then Emily would be in seventh heaven, I suspect. In fact, it might even overcome her own hesitation to produce biological children of her own. Or, of course, she could complete the sublimation of her own maternal instincts by investing them all in a child of Honor's and Hamish's.
Just have to see what happens, won't we?