häçking into someone's Facebook account is îllégâl and unethical. Instead of resorting to such actions, you should report the situation to Facebook immediately. You can report the threatening messages and the individual who is attempting to blackmail your relative. Facebook takes these matters seriously and will take action to protect your relative and their account.
Encourage your relative to secure their account by changing their password, enabling two-factor authentication, and reviewing the account's privacy settings to make sure it is as secure as possible. Remind them not to engage with the blackmailer and to report any further harassment or threats to the authorities.
It's important to handle these situations responsibly and within the boundaries of the law. It's always better to seek help from the proper authorities and platforms like Facebook to address these issues.