All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam , is His slave and Messenger.
First of all, we would like to thank you for being keen on wearing Hijab and for admonishing your husband to do good and forbidding him from doing evil, especially in regard to performing the prayer. There is no doubt that these are among the best actions by which you get closer to Allaah, so keep on doing this.
You should not seek the pleasure of anyone by giving up your Hijab, be it your husband or anyone else. For more benefit on Hijab, please refer to Fataawa 89815 and 96283. Also, for more benefit on a husband who does not perform the prayer regularly, please refer to Fatwa 88016.
On the other hand, you should know that it is Islamically permissible for a husband to marry more than one wife if he is able to be just between them; Allaah has the absolute wisdom in legislating this. For more benefit, please refer to Fatwa 81469.
The fact that the first wife is not negligent about the rights of her husband has nothing to do with the issue of the husband taking a second wife. As regards the husband spending on his wives and being just between them, then this is a matter which only the husband knows. But of course, if he is already negligent regarding one wife and her children, then it is more likely that he will be negligent with two wives if he marries another one.
As regards the father objecting to this marriage, then the son is obliged to obey him in this if he has a sound reason for refusing, otherwise there is no obedience to him. There are some conditions in regard to the obedience of children to their parents, and this is discussed in Fatwa 84942.
Concerning your statement “…and keep relations with the girl”; then if you mean a relation within a valid marriage, then yes, but if it is just an affectionate relationship between them without marriage, then this is Islamically forbidden.
As regards him being affected by some magic, then if you predominantly think that he is affected by it, then the treatment for this is Ruqyah. For more benefit on Ruqyah, please refer to Fataawa 82918 and 88660.
Indeed, reciting the Quran on water and giving it to your husband to drink is permissible and it is a kind of Ruqyah.
Finally, it should be noted that each spouse is required to have a marital relationship with the other on reasonable terms, and to fulfill his/her rights towards him/her. Allaah Says (what means): {And due to them [i.e. the wives] is similar to what is expected to them, according to what is reasonable.}[Quran 2:228]
Allaah Knows best.