What is the ruling regarding a wife remaining with her husband who was committed to religious practice but then changed, becoming remiss in his faith, and now demands anal sex from her, threatening her with infidelity if she does not obey him, while she fears divorce due to her inability to work (wearing a niqab) and support her children?

You must advise your husband and remind him of the righteousness he once embodied, and the danger of the sins he is now committing and his abandonment of prayers. Anal intercourse with a wife is forbidden by the consensus of the majority of scholars, and you are not permitted to enable him to do it. If he threatens you with it, do not obey him; for "there is no obedience to a creature in disobedience to the Creator." Sustenance and shelter are from Allah, and whoever fears Allah – He will make for him a way out and provide for him from where he does not expect.