What is the ruling regarding the second husband divorcing his wife after the first husband divorced her sister in a Shighar marriage, and is it permissible to rectify the contract by paying the dowry, and what is the ruling on adding a small amount to the contract to change it from a Shighar marriage?

Divorce occurs in an invalid shighar marriage according to the majority of scholars. This is an irrevocable divorce. The divorcing husband is obligated to pay the mahr al-mithl (A customary or fair dower) if the divorce occurs after consummation or khalwa (valid seclusion). Paying money after the contract does not validate an invalid shighar marriage, unless a Sharia court rules it valid. If the mahr (dower) is named in the same contract, this is called a "form of shighar," and it is valid according to the majority of scholars, provided there is no explicit condition of exchange between the named mahr and sexual intercourse, and that a small mahr is not a trick to circumvent explicit shighar. It is advisable to avoid disputed forms of shighar to protect women's rights.