Praise be to Allah.
A man has to strive to guide his wife and encourage her to do the duties that Allah has enjoined as much as he can, because Allah says (interpretation of the meaning):
“O you who believe! Ward off yourselves and your families against a Fire (Hell) …”
The great scholar Abu Bakr al-Jassas (may Allah have mercy on him) said in Ahkam al-Quran (3/697): This indicates that we have to teach our children and wives religion and goodness, and whatever is essential to good manners.
This is supported by the words of the Prophet (peace and blessings of Allah be upon him): “Each of you is a shepherd and each of you is responsible for his flock.” It is well known that just as a shepherd is required to guard and protect those under his care, he is also required to discipline them and teach them. End quote.
The great scholar Ibn Katheer (may Allah have mercy on him) said, commenting on this verse: Qatadah said: He should enjoin them to obey Allah and forbid them to disobey Allah. He should take care of them as Allah has commanded and enjoin them to obey Him and help them to do so. If you see any disobedience to Allah, you should rebuke them for that. End quote.
If the brother has done the marriage contract with this woman, then she is his wife and he has to strive to teach her about her religion and help her to learn, but kindness and gentleness should be the method he uses in achieving this aim. The Prophet (peace and blessings of Allah be upon him) said: “When Allah wills good for the members of a household, He introduces kindness to them.” Narrated by Ahmad; classed as saheeh by al-Albani in Silsilah al-Ahadeeth al-Saheehah (3/219).
He has to stop her doing that which will harm her religious commitment, such as listening to misguided du'at, if what they promote is misguidance and scholars whose religious commitment and knowledge is trustworthy have warned against them. This applies if she is unable to distinguish between truth and falsehood. But if she knows what is true and there is no fear that she may be influenced by what the misguided du'at say, then there is nothing wrong with her listening to them and accepting what is true and ignoring what is false. This applies to the innovations that the scholars have denounced and warned against. As for issues where there are differences of scholarly opinion where ijtihad is allowed and the scholars have different points of view, it does not matter if the ordinary person follows one of them.
To sum up: You have to protect your wife from misguidance and following whims and desires, but you should be gentle with her, and try to convince her that people do not accept falsehood unless it is mixed with truth so as to confuse them. If she understands this, she will be convinced, in sha Allah. You should also try to provide a suitable alternative from du'at and scholars who are trustworthy with regard to their religious commitment and knowledge, and who attract people by their good presentation skills. You will find many of this type, praise be to Allah.
May Allah help us and you to do that which He loves and which pleases Him.
And Allah knows best.