I wanted to sell a plot of land I own. Some of my relatives, with whom I have strong family ties, wanted to purchase it from me. My neighbor objected claiming that he has right of preemption and therefore has the primary right to its purchase. What is the opinion of the Shari'ah on this? Will I sin if I give preference to my relatives over my neighbor?

The majority of scholars agree that preemption is restrictive and not comprehensive since it contravenes the established principle that one may dispose of his property as he wishes. According to them, a partner and not a neighbor is entitled to preemption; according to Hanafi scholars preemption is permissible to a neighbor; while according to some Hanafi scholars, it permissible to whoever shares the utilities such as the same entrance, access to water, the access road, and the like.

Based on this and in reference to the question, the neighbor does not have the right of preemption because he is not a partner. The authority in Egypt favors and supports this opinion in accordance to Article 393, paragraph (B) of the civil law which states:
"Preemption is not permissible in a sale involving parents, ancestors, or offspring; spouses; relatives up to the fourth degree; or between in-laws up to the second degree."

The above article is the reason that judges today do not consider the aforementioned scenario to fall under preemption. Since its issue, the law of preemption was based on the Islamic Shari'ah; even if it has assumed the nature of the conventional legislation which is considered a kind of choice or ijtihad in the Islamic Shari'ah, it must be followed since the leader's verdict eliminates differences in opinion.
Allah the Almighty knows best.