What is the ruling on someone who entered into a shighar marriage, then wanted to divorce his wife with a reciprocal divorce, so a non-adult wrote a divorce document in which the names of the two wives were not mentioned, and the two men signed it without the intention of divorce, but rather out of fear of being killed?

Merely signing the divorce paper does not constitute a divorce. Divorce only occurs through explicit verbal pronouncement or writing it with the intention of effecting it. As for Shighar marriage, it is forbidden. It is when a man gives his female ward in marriage to another man on condition that the latter gives his female ward in marriage to him, without any dowry exchanged between them.