Actually, from Ewen's POV it would in some sense be good if Alison was pregnant, if he's going to die! Because then he would have an heir (well, at least if it was a boy). I'm sure Alison is brought up to see this as an important charge

Well, quite so! He'd have his ~legacy~. But from a woman's pov, having a child in wartime is always a big gamble, hence the baby boomers. If there were repercussions including attacks on homes, she'd be in real serious trouble.