Sorry about the twins thing, I have 3 friends, one of whom had identical twins and 2 who had fraternal twins. Obviously none of these were planned twins and all natural conception so a bit of a shock 
A couple of things to consider, firstly that parents doing childcare can be fraught with issues, or in my sister's case my Mum was amazing but was then diagnosed with terminal cancer and died a few months later. She was early 60s.
Secondly, you can never work from home whilst looking after a child, it is almost impossible long term.
The other issue to consider is if your child has additional needs you might not be able to put them into childcare depending on those needs.
I don't know how child friendly your workplace is, one of my friends with the twins was made redundant whilst pregnant which just made the decision for her as she didn't think she would be able to return to work.
And no, the mortgage company cannot suddenly change your terms and conditions because you had a child.
I just like to cover all bases. The probability is that it will all work out somehow like most of us, it just does. You find a way to make it work. But the childcare impact on your finances massively reduces your joint income hence why everyone is saying get a house before having children.
If you are looking for a mortgage, I can recommend London and Country who are recommended by Money Saving Expert. Just browse their site for ideas of lending and cost per month.