Sorry, haven't RTFT but I just wanted to say, that the children have TWO parents and the financial responsibility does not fall solely on the father to provide for the DCs. Whilst he should absolutely pay maintenance when he is working, he also has the right as a parent to stay home and provide care for his child/children.
If XW does not work because she is providing care because she had no choice but to stay at home, she now has the option to return to work. If she choses against that option, that is her choice, but she cannot force XH to work just to pay her bills. It's not like he chose to leave a good job, he was made redundant.
The moral obligation is for the mother AND father to provide for their children according to their means. The CSA will no doubt take the household income of the NRP in to account, not just the fact he is not working. From Citizens Advice -
"If you have no income or a low income
You’re expected to pay some maintenance even if you’re unemployed or on a low income and even if you're already paying maintenance for other children. Generally how much you have to pay depends on your income – it doesn’t matter what other expenses you have."
So NRP will still have to pay from household money, but at a reduced rate.
It should not be only women who have the choice to stay at home and care for their children.