Regarding the story that someone mentioned that
he agreed with his uncle to marry his sister to the uncle's son for a defined Mahr (mandatory gift to a bride from her groom) to be paid within a period of three years. After the elapse of this year, he asked his uncle to give him his daughter in marriage for an independent Mahr.
The person asks whether this is considered Shighar or quasi-Shighar.
(Part No. 18; Page No. 427)
If the reality is as mentioned in the question, it will be unobjectionable provided that there is no partiality or trickery and the Mahr of any of the two wives is not decreased in view of the Mahr of the other. Moreover, marriage as such is not considered Shighar or quasi-Shighar. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.