All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We supplicate Allah to make us steadfast on His religion till we meet Him while he is well Pleased with us.
Dear sister, praise be to Allah for guiding you to the right path. No doubt, it is the greatest blessing of Allah upon a human being. So, after receiving this blessing nothing should bother you.
Thereafter, we advise you to strive to call your children towards Islam, showing them the merits of Islam, bringing to their knowledge that Islam is a source of happiness in this life and the Hereafter as well. Conversely, disbelief is the source of misery and destruction in this life and the Hereafter.
Know that your husband is not obliged to spend on the children who are not from him; if he does it voluntarily, then that is a highly appreciated voluntary act. The real father of the children is responsible for spending on them. If he is not available, then you should spend on them till they reach the age of maturity.
We advise you to openly discuss this issue with your husband and try to convince him by informing him about the great reward he will get if he takes care of his stepchildren and spends on them even though he is not responsible for that. However, being free from spending on them does not mean in anyway being harsh with them or hurting their feelings.
Nevertheless, we advise this person (your husband) to be kind with his wife and her children. Also, we remind him of the Prophet’s behavior with his wives and with his stepchildren. Umar ibn Abu Salamah who was the stepson of the Prophet narrated: “I was a boy under the care of the Messenger of Allah and my hand would wander about in the dish. The Messenger of Allah said to me: ‘O boy! Mention Allah's Name (i.e., say Bismillah before you start eating), eat with your right hand, and eat from what is near to you.’ Since then I have applied those instructions when eating." [Al-Bukhari and Muslim]
The Prophet also said: “The best of you are those who are best to their wives.” [Al-Tirmithi]
We supplicate Allah to solve your problems, ease your matters, bless you, and open the hearts of your children for Islam.
Allah knows best.