Think you need to do a budget/financial audit type thing together with your DP.
Look at the current outgoings and incomings, then try to cost how they'll change in different scenarios (you staying in London and DP travelling from Newcastle, you moving to Newcastle and travelling to parents, you working full-time/part-time or being a SAHP).
Look into tax free childcare, and actual nursery/childminder costs in both London and Newcastle. Think longer term than just 2 years, perhaps by keeping a part-time job now you will be able to earn lots more in 5 years than if you'd been a SAHM.
Look into coach travel - usually lots cheaper than train (MegaBus, National Express).
Engage with your DP to try and figure it out as a family. It sounds a little like he's been given all the financial stuff to figure our and you're whining that he won't let you do things, when in fact there's just not the money. So step up and figure it out.
If he doesn't let you engage like this, and instead prefers to keep you in financial control. Red flag for financial abuse. But you might find him willing.