I would imagine Kieras parents are still working full time themselves tbh, they dont strike me as being well off enough to retire early etc.
I understand the frustration though, they've always planned to have multiple kids and his conditions are not new, there's long term planning for babies but not for financial security - she's only just starting little doe up really and lanas over 1, it sucks but wouldnt you return to work sooner? Lots of people who work outside the home have to return before a year because of money, self-employed people in my experience are back sooner. Has Alex ever mentioned retraining or going to college to try and get a career where he might have more flexibility?
Editing just to say: that came off as super unsympathetic and ofc its not as simple as 'he should just retrain' with disabilities, its just frustrating that they are still youngish people and he's changed jobs a lot so why the rush to have a baby when things have never been that stable. His workplaces should of course be following reasonable adjustments and he shouldnt have to worry that his disability would impact his job, but sadly due to his conditions it might be that his time off in the past has reached a point where even reasonable adjustments cant enable him to continue being employed if he's still missing a lot of work. I really hope that hasnt been whats happened as that would be horribly demoralising, even if it is legal.