Well, has he not spun a nice little web around you. Gets you out of your own Country and moves you to his then ....
He controls all the finances, sets you up in a nice detached property where you get comfortable, gets you pregnant twice, moves you and then, tells you nothing is now affordable because of his job.
Admittedly that would be correct moving from Liverpool to London in that there is absolutely no way you could afford a detached property however, certainly something could be within your budget and a two bed terraced house will not loose its value if bought in the right area. I would also question that there are no moving fees etc. allocated by the employer as this is normal in some occupations.
You could equally move out of London by a half hour where prices are significantly lower than London prices. Some parts of Essex for example are only a half hour to Stratford where there are Tube and DLR lines.
The fact he wants you now in the control of his parents house raises major red flags for me and, I am very surprised not one person on here has questioned that given your Religious background.
How sad that there is not one person on here that will question what is happening to you. Shame on you all.
You sound like you have no idea of your finances yet, somehow managed to have signed for a mortgage that allowed for a detached property originally unless that is not the case. I cannot see anywhere on your posts that you say you work.
I would be very very careful now about what you agree to. It sounds like your children were born in the UK and that also needs to be considered. Your chances of going back to the US sound very slim and I am very sorry for you for that.
If there is anyone on here that could give proper advice, offer some links for this lady please do that. There must be someone.