They generally don't try to have children when the population's maxxed - in VV3, if you try to make them, you'll get a message about not enough housing. Much different from humans, that way.
They also GENERALLY don't parent if a different skill is checked, though there are exceptions - especially if there are no tasks for their chosen skill, or they have no skill selected, or no skill in the selected skill. In those cases they just do what they know how to do.
