Is it permissible to offer chicken instead of meat for a vow (nadhr), and is it permissible to give the vow's portion of a disobedient brother to the poor?

Fulfilling a vow is obligatory according to what was specified in the text or intention. Therefore, it is not permissible to substitute chicken or duck meat for lamb or goat meat if the latter was vowed, because it is a deviation from what was vowed to something inferior. However, if one vowed to donate meat in general, then he may donate chicken meat, because it is considered meat.