Am I allowed to prevent my wife from visiting or contacting her family, given the repeated harm and ongoing conflicts with her stepfather, and would I be blamed for that?

Among the objectives of Sharia is fostering harmony and affection between Muslims, hence reconciliation is encouraged. Allah the Almighty says: "And reconciliation is better."

Our advice is for you to strive to mend your relations with the cooperation of influential people. Remember that discord is evil, for the Prophet, peace and blessings be upon him, said: "The gates of Paradise are opened on Monday and Thursday, and forgiveness is granted to every servant who does not associate anything with Allah, except for a man between whom and his brother there is animosity. It will be said: 'Wait for these two until they reconcile.'"

Each party should pardon and forgive. Allah the Almighty says: "And those who pardon people." And the Prophet, peace and blessings be upon him, said: "And Allah does not increase a servant in anything due to forgiveness except in honor."

If the dispute continues, do not prevent your wife from maintaining ties with her mother, for a husband does not have the right to prevent his wife from visiting her parents. You would be blamed for preventing her as long as there is no legitimate justification, and do not punish her by depriving her of ties with her mother. If you fear harm from her visiting her mother in that man's house, then you may prevent her from visiting her mother in that particular house, but do not prevent her from visiting absolutely.

There is no blame upon you for not visiting them as long as it leads to harm.

Regarding the existence of a relationship between the man and the girl, if it is proven and you fear harm, inform her guardian so that he may protect and safeguard her, and do not mention the man's name to him.