What is the ruling on purchasing a car or metals from the bank through the methods mentioned? And can my fifty-year-old mother, who is in her 'iddah (waiting period) and whose menstruation stopped after one menstrual period, marry directly, or must she wait for three months?

Purchasing a car through a bank takes two forms. If the bank sells metals to an individual on credit for a price higher than their market value, and then the individual authorizes the bank to sell them, there is no harm in that. As for the mother's iddah (definition) (waiting period), she should ask the women of her age when their menstruation ceases and they despair of it, and she should be like them. If despair of menstruation occurs for them at fifty years, then her iddah is three months, based on the Almighty's saying: ﴿And those women who have despaired of menstruation among your women - if you doubt, then their waiting period is three months﴾ [At-Talaq (definition):4]. If they despair at an age older than that, then she is like them, with the maximum being sixty-two years. If she has already observed part of her iddah by menses and then despaired, she must restart the iddah of one who has despaired, which is three months.