Is it right for a husband to conceal the news of his wife's pregnancy from her family until the fifth month—using the pretext of the hadith "Seek help in achieving your affairs by discretion"—while the wife wishes to share the news with her family?

If your family is trustworthy and you do not fear any harm from them, you can try to persuade your husband to allow you to inform them about the pregnancy. The hadith (definition) your husband mentioned is authentic, with the wording: "Seek help for the success of your needs through concealment; for indeed, every person of blessing is envied." If your husband is not convinced and does not permit you to inform your family, then it appears that you must obey him, as this falls under marital affairs in which obedience is obligatory. Some scholars are of the opinion that a wife's obedience to her husband is obligatory in everything that does not involve disobedience to Allah.