What is the expiation for an oath of divorce if I swore to my wife that she would not speak to my brothers, and then I reconciled with them and wanted her to speak to them?

The majority of scholars hold that whoever swears by divorce and then breaks their oath, their wife is divorced, whether they intended divorce or merely a threat. However, some scholars, like Ibn Taymiyyah, are of the view that if one swears by divorce for the purpose of threatening or emphasizing something, they are only liable for an expiation for breaking an oath (kaffarat yameen) and their wife is not divorced. The adopted fatwa is that of the majority. Therefore, if your wife spoke to your brothers, she is divorced. If you wish to permit her to do so and you have not divorced her more than once, then permit her and then take her back (raj’ah). It must be noted that the permissible oath is by Allah Almighty, and swearing by divorce is among the oaths of the dissolute and has grave consequences.