Is it obligatory to inform the girl and her family about the young man's inability to procreate after a unilateral orchiectomy, even with an attempt to treat the other testicle and store sperm, out of fear of the marriage being rejected or the news spreading, and to safeguard the girl's right?

If good fortune befalls a believer, he gives thanks, and if adversity befalls him, he perseveres, and both are good for him. Marriage is a source of tranquility, affection, and mercy. The suitor must inform the fiancée about matters concerning procreation if he is certain of his inability to have children. As for your situation, since the scans have not yet confirmed anything, you should supplicate to Allah, perform other tests, instill confidence in your brother, and accept Allah's decree. For Allah grants children to whom He wills and makes barren whom He wills, and hope in Allah is great.