In all cases, the relatives and parents of such heirs would try to find ways to get the heir cured, if this did not work, it would get complicated. in the case of a child diagnosed like Katherine and Nerissa Bowes-Lyon, the heir would be deprived of the right to inheritance and the parents would have to have other children, but these children with such a diagnosis would not be killed, but instead would go to some military camp and be forced to train and fight in some war or something, And if they died, at least they died in some war or battle, (in their view this was a very positive point) and stories would be invented about how they overcame such difficulties and such, and whoever said that these heirs were not warriors, would be killed for treason and worse. Reputation is very important for the mc’s family.
In the case of Alexei and hemophilia, these heirs would be obliged to study very, very hard about strategy and everything else that involves knowledge, since they would not be able to fight or train because of their condition. And if they could not live up to their parents’ expectations and failed, both in this and in not being able to have children, they would probably be killed. After all, in their minds a member of their blood who cannot overcome his “weaknesses” is not a sign of having their last name or even staying alive.
In other cases of other diseases and diagnoses,It is the same as these previous ones, if the heirs who had such things could not overcome such “weaknesses”, they might end up being killed or even forced to fight in battles, even if they don’t know how to fight exactly.