What is entailed for someone who vowed to fast a consecutive month if they masturbated, and then did it, and then vowed to fast two consecutive months if they did it, and then did it? And is it permissible for them to fast Sha'ban and Ramadan consecutively if they owe fasts?

The vow made by this person is a vow of obstinacy or anger, and it is not obligatory to fulfill it. Its maker has the choice between fulfilling it or paying the expiation for an oath (kaffarat yamin). This is the more preponderant opinion, and he owes two expiations for the two vows. If he wishes to fulfill it, he must fast for three months: one individual month and two consecutive months. Fasting Ramadan cannot be included within them, nor can fasting Sha'ban and Shawwal, because the continuity would be interrupted by Ramadan. He must fast the two consecutive months either before or after Ramadan.