Praise be to Allah.
First of all, we would like to congratulate our sister for embracing Islam, which is the joy for which wealth and souls would be sacrificed, for all the blessing of Islam makes all grief and distress fade into insignificance.
The sister says that she loves a Muslim man. We say: it is not appropriate for a Muslim woman to fall into the trap of nonsensical emotions and forbidden relationships into which others fall. The love which people hear about and read about is one of the dazzling tricks of the Shaytaan, and it usually happens with regard to things that Allaah has forbidden. If a man finds that he likes a girl, the only option he has is to ask her guardian (walee) for permission to marry her.
The mans mothers comment that new Muslims cannot be good Muslims is false. Were the Sahaabah (may Allaah be pleased with them) anything but new Muslims, given that prior to their Islam they had been believers in Shirk? Does any Muslim have any doubts about their commitment to religion and their character? Moreover, we see that many new Muslims are many times better than many (born) Muslims! Just because a Muslim is new does not mean that he will never be good, and just because a Muslim is born in Islam does not mean that he is good. What counts is Taqwa (piety, awareness of Allaah) and righteous deeds, as well as the length of time one has been in Islam and has been worshipping Allaah.
There is no reason why knowledge of the man's marriage should not be withheld from his parents, especially since this is in the interests of the sister and there are so few people who can help her to overcome her difficulties. It is the woman who needs a walee according to shareeah, not the man. However, we would prefer that he wins his familys approval by convincing them, because this is in their best interests, benefits which may be lost if they find out that their son concealed his marriage from them.
The fact that the husband says he wants to call the children to Islam is good. We ask Allaah to help him to achieve this. The fact that the Hindu father is evil is sufficient reason for him not to make an open display of his calling the children to Islam, if that could lead to this kaafir taking the children away by going to the kaafir courts. You have to act with wisdom in this case.
The woman who is asking this question should not arrange her own marriage even if she has been previously married, because shareeah does not permit this. If she does not have a walee as required by shareeah, then her walee may be the qaadi (judge) or whoever is in charge of the Muslim affairs in her country, such as the head of the Islamic centre or his deputy.
They especially the sister have to seek the help of Allaah in dealing with these problems which are giving her sleepless nights. Everyone should know that whoever puts his trust in Allaah, Allaah will show him a way out. She has to make duaa sincerely, and he has to try as hard as he can to advise his family and change their views about new Muslims by showing them real examples of people who are the opposite of what they think. With regard to the tragedy caused by the former husband, we advise her again not to make an open display of her calling the children to Islam, lest that should cause the father to do something that will have bad consequences. If they feel suspicious about his intentions, there is no harm in calling the police to do whatever is necessary with regard to him.
If getting married means that the sister will lose her right to custody of her children, we advise her not to get married now, for fear that these two souls may end up in Hell in the Hereafter unless she fears that she herself may commit some immoral action, in which case she should marry the Muslim man whom she has told us about, with witnesses and a walee as we have stated above. Publicizing the marriage is sunnah, although it does not have to be announced officially and in writing. But this sister has to live in a protective Muslim environment and those people will have to know about her marriage lest she bring upon herself gossip about her honour. If it will be better for her to leave the place where her ex-husband lives and move to another place where she can be free, have custody of her children and be able to marry a believing Muslim man who will protect her and her children, then she should do that.
She has to make duaa and turn to Allaah to relieve her distress and grief. We pray that Allaah will give her the strength to do that which He loves and which pleases Him.
And Allaah knows best.