How does one fulfill a vow that involves slaughtering a ram or offering food to the mosque? Is it permissible to pay the value of the food in money, or to fulfill the vow upon the brother's wedding? And are the current problems due to not fulfilling the vow?

Fulfilling a vow (nadhr) is an emphasized obligation. Therefore, the questioner must fulfill her vow by slaughtering a ram and offering food to the people of the mosque. It is not permissible to give the vowed offering to a different party than the one specified, nor to substitute something else for the vowed item if the original is available. This is based on the Prophet's (peace be upon him) saying: "Whoever vows a vow that he can fulfill, let him fulfill it," and his saying: "Whoever vows to obey Allah, let him obey Him." Any problems that may arise are not necessarily connected to the non-fulfillment of the vow, though abandoning an obligation is one of the causes for incurring punishment.