Is it permissible for siblings to abandon their brother and his wife who have been disobedient to their parents and caused problems, and to limit interaction with them to the narrowest scope without a complete boycott?

If the situation is as described in the question, then it is permissible to abandon one's parents if such abandonment leads to their repentance. Abandonment is permissible for those who openly commit major sins if it serves a predominant شرعية (Shar'i, Islamic legal) benefit. It is sunnah (recommended) to abandon those who openly commit verbal, physical, or doctrinal sins. Abandonment is permissible if its purpose is to discipline and deter the disobedient, especially if it leads to their reform. It is not permissible for a Muslim to abandon his brother for more than three [days], unless there is a fear that associating with him would corrupt religion or cause harm. Abandonment is not an end in itself; rather, it is a means to reform the conditions of people. Thus, it is good or obligatory if it leads to the disobedient person ceasing their disobedience. However, if association is the means to achieve the benefit, then it is preferable to abandonment.