No doubt you'll get lots of opinions, here's mine.
Start living on one salary now. See how you would cope if you started a family. The other salary can go to increasing your savings to cover maternity expenses.
Separately, keep 3-6 months cash for emergencies. As a public service worker you are not going to lose your job, so decide how much this would need to be.
Work out how much the 120k mortgage needs to be reduced so that the rent would cover its mortgage..
This would take the pressure off a single salary to cover 2 mortgages, you'd have a rainy day fund plus a maternity fund.