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.
What you mentioned in your question is the rule set by the scholars that having children is a right for each of the spouses, and neither of them can refrain from it without the consent of the other spouse. Ibn Qudamah said while he was explaining the rule of “Al-’Azl” (ejaculating outside the vagina as birth control): “as the wife has the right of having children, and Azl harms her, therefore, it is not permissible without her consent.”
Your husband’s need to raise up his children (from the other wife) does not give him the right to prevent you from having children, if the two spouses need to control the birth, it should be upon mutual consent, and the husband should not force his wife to do so.
We advise you to talk to your husband in a cordial manner, and you may also ask some people who are so close to him to speak to him so that they may help you in persuading him to give you such right.
Allah knows best.