To answer your question, 25% seems a big increase, but if there have been several years of no increases I'm not surprised. That's effectively his gross profit before tax, his net hourly pay will be considerably below that once he deducts tax and NI, holiday and sick pay (if he can afford those), pension contributions, overheads, petrol, marketing, cancellations etc.
My unsolicited advice (sorry if not helpful): I'm surprised your Diocese doesn't cover your council tax, water and buildings insurance. The PCC(s) should also be paying expenses to cover part of the broadband and heating bills, unless one of the Churches has an office your DH works from. You should be able to claim tax back as well if he has a home office/ PCC meetings in the Dining Room etc. Our PCC also pays reasonable travel expenses/mileage (for visiting parishioners etc., not driving to your place of work to take a service).
Unite have a branch for ministers of religion, I suggest he joins and asks for advice on whether his situation is fair.
I also don't understand why he is constantly 'on-call'. Ok, if someone is dying he might need to rush off, but most Vicars I know keep office hours, and most take Saturday and one day off in the week. It's dangerous not to, frankly, you end up being at the beck and call of people who don't really need your help otherwise.
Other than that, your situation doesn't sound that different to a lower income family with a newborn. Once the child is old enough, you will also need to get a job. All the spouses of married Vicars I know have jobs of their own.
Well done on keeping the flat. Hopefully over a long career, capital value increase alone will give you a bedrock for a retirement property.
Final point- it's not ideal perhaps, but if it really is a struggle a few Vicars I know have utilised their big vicarages by taking in a lodger or two. Obviously, with small children you'd probably want a level-headed, mature woman- but it's worth investigating as an option. You'll need permission from the Diocese, but they shouldn't withhold that unreasonably- you need to ensure they stay on the kind of licence tenancy that means they can be quickly evicted.