What are the implications of swearing, vowing, and imposing a prohibition after intense anger by saying: "I vow to God that I will not attend, and it is forbidden for me just as Mecca is forbidden for Medina, and I vow to God, and I swore that I would not go to my brothers' weddings"? Is expiation (kaffara) obligatory, what is its amount, and how is it paid if one is unable to fast, especially with prior uncompleted fasts to make up?

Not attending a relative's wedding without a legitimate Shar'i (Islamic legal) reason is considered makruh (disliked) or haram (forbidden) because it severs kinship ties. If you swore not to attend, then attended, you owe a single expiation for breaking an oath (kaffarat yamin wahidah), according to the majority of jurists. It is recommended for you to expiate your oath and attend the wedding. As for delaying the making up of missed Ramadan fasts until the next Ramadan without a valid excuse, you must pay a fidyah (expiatory feeding) for each day, which is one mudd of food. This fidyah does not multiply with the repetition of years. It is permissible to give the fidyah to one needy person or more, and it is permissible to feed them before, after, or concurrently with making up the fasts.