Does boycotting a brother who fraudulently seized his siblings’ inheritance, with the participation of some siblings, constitute a severing of kinship ties, and what is the solution in this case?

It is permissible to shun disobedient Muslims for more than three days in order to rebuke them and encourage them to abandon their disobedience. However, if shunning does not yield the desired results, but rather produces an adverse outcome, then it must be abandoned, and another method should be employed to win over the heart of the disobedient person. It is sunnah (definition) to shun those who openly commit sins, whether they are physical acts, verbal transgressions, or deviations in belief.