NEW HOUSE

UnderOffer

Why do YOU want to move? I’ve read your wife would like a detached, new build, but what reasons would YOU move for? Is the house closer to either of your jobs?

Your post portrays your wife as quite materialistic in that it seems she is trying to keep up with friends and their luxuries. This move does not bode well, particularly that she wasn’t happy to increase hours to cover some of the increased costs.  

You need to be firm and clear and have a sensible conversation outlining your concerns and increased costs and what ifs I.e. redundancy, ill health etc., don’t over commit, look at all options and compromise, you might find something cheaper, nearer but perhaps is detached that you’d both be happier with. 

thegreenone

A lot of new builds have little/if any, in-built storage which will mean buying your own and reducing m2 in the bedrooms.  The sizes may look good but once you add in wardrobes, COD's and desks etc.........
Is the development within easy reach of bus/train?  If not, as your children grow older, you will both be taxi-service, which will limit their activities/social life and yours.
Would your children be happy to move schools?  Obviously, this one can't be asked directly yet.
If the children want to stay at their current schools, how much extra travelling would this entail?
Will you be living in a building site once you move in? Is the developer building more nearby?
Will there be a charge for the communal areas and developer-led constraints/covenants?  If you live Freehold now, you are going backwards with this.

Lots of things to consider.

In the early nineties, I was desperate to move out of our three story townhouse/tiny garden - we had two young boys.  Hubby was the voice of reason but did agree to go and see a new development just behind us.  Wake up call.  Yes, all new shiny-shiny, slightly larger garden and more rooms but, oh my, those rooms were a lot smaller than we had.  We sold in 1995 and moved to a 3-bed detached bungalow with a lovely garden.  I'm so pleased we waited.

markin

Go part time and live for the moment! She can work full time till shes 70 if she wants.

If you over pay for 5 years, you could have it paid off early, And after the kids leave you will be wanting to down size anyway.  

Ath_Wat

I still haven't seen the OP outline the actual reasons his wife is giving to want to move.  People have speculated but the OP has confirmed nothing.

When you tell her all the downsides you have listed to us, what does she actually say?  Without knowing whether she has reasons you haven't told us about yet that all people can do is speculate.