All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The relation between husband and wife should be built on mutual love, kindness and understanding. So, any problems that arouse between them should be treated in a friendly way. So, we advise the questioner to fear Allah, The Almighty, obey His Orders and stay away from anger and its causes. Imam Al-Bukhari reported that a man said to the Prophet : “Advise me”. The Prophet said: “Do not get angry”. The man repeated the same request and the Prophet kept on saying to him: “Do not get angry.” Know also dear brother that the Sharee’ah prescribes some duties and rights that should be honored by each spouse towards his/her partner. So, if Allah has ordered the woman to obey her husband, He has also ordered the man to keep good company to his wife.
Allah Says (what means):
• {And live with them in kindness. For if you dislike them - perhaps you dislike a thing and Allah makes therein much good.} [Quran 4: 19]
• {And due to the wives is similar to what is expected of them, according to what is reasonable. But the men have a degree over them [in responsibility and authority]. And Allah is Exalted in Might and Wise.} [Quran 2: 228]
It is unlawful for the husband to oppress his wife or beat her unless she refuses to let him enjoy sexual intercourse and only after having admonished her and deserted her in bed. Now, if he knows that beating is the only solution, he could beat her lightly. As for your oath to divorce her whenever she talks to her brother, this is called conditional divorce. So, if your intention was that she is divorced as soon as she talks to her brother, she will be divorced if this condition is met. There is a consensus of scholars over this issue. But if your intention is just to deter her and to emphasize that she should stay away from her brother, then the scholars differ over this issue. The majority of the scholars are of the opinion that she is divorced anyway as soon as she talks to that brother. But some scholars are of the opinion that in the last situation, she is not divorced considering that this is an oath that should be expiated like any other oath. Now, if we consider that she is divorced according to the first opinion, then her divorce is a revocable one. So, you can return her to wedlock life without her consent or the consent of her Wali (guardian) and without witnesses.
With regard to your question “shall I divorce her?”; we do not advice any husband to divorce his wife, as divorce is the lawful act which Allah hates most and it should be the last resort. Now, if no solution is possible and if reconciliation becomes impossible, then one could divorce. But one should always have in mind his children's education and future. If she is the one who insists being divorced, you can accept Khul’ from her; which means accepting financial compensation from one's wife and divorcing her for that. Finally, we advise this wife to fear Allah, obey her husband as his obedience is an obedience to Allah, and think about her children's future. Imam Ahmad reported that the Prophet said: “If I were to order any person to prostrate to anyone else (other than Allah), I would have ordered the wife to prostrate to her husband.” Ahmad also reported that the Prophet said: “If a woman prays her five obligatory prayers, fasts her month (Ramadan), keeps her chastity and obeys her husband, it will be said to her (on the Day of Judgment): enter Paradise by any gate you wish.”
Allah knows best.