My husband has several children by his first wife, and two by me, his second wife. We are both Muslim. Neither of us knew of the other's existence for many years. For over four years now we knew we share the same husband. His first wife refuses to accept his second marriage and uses the well being of the children to blackmail my husband from being just. She has also been insulting to my children. The first wife has had one incident of mental depression for which she was hospitalized briefly before the conception of their first child fifteen years ago. My husband feels she is not mentally stable and feels pressured to conceal any time spent with us. Since, her awareness of the second marriage he has spent 1year being fairly just and 4years conceding to her demand, to have no normal relations with us. What impression wills this have on my children seeing their father behave in what I feel is an un-Islamic manner. They are suffering due to his absence. Please advise me on what steps I should take? Her persistence has caused us to divorce once, now we are reunited. I fear her actions will be detrimental for both our families.

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

We advise our questioner sister to be patient for the ill treatment of her co-wife and the injustice of her husband. She should try to handle the matter with wisdom and kindness, taking into consideration the condition of the first wife who is in need of special treatment rather than acting in haste.
On the other hand, for the children's interest keep good ties with your husband since splitting of a family leads to a great loss for children.
At the same time we advise the husband to fear Allah and to implement the Commands of Allah especially concerning the matter of justice with wives. We remind him of the Hadith that the Prophet (Sallallahu Alaihi wa Sallam) said: "When a husband has two wives and does not act justly between them, he will come the Day of Judgment with a side of his body hanging down" . [al-Tirmizi]
The husband should know that the lack of the knowledge of his first wife of the second wife and her mental illness do not justify his behaving unjustly toward his second wife.
We ask Allah to guide all of us to the right path.
Allah knows best.