How Can You Make A Friend Your Legal Brother?

After all parents have passed away, the only way to make someone your legal brother would be to find someone willing to legally adopt both of you. However, there is no real legal benefit to someone being your brother that could not be handled through other legal documents such as wills and medical directives.

That would depend on whether or not your parents are willing to adopt them. However, it is a long drawn out court process and it requires the prospective parents to let themselves open to a lot of personal information which they may not be willing to share, and interviews in the home by the social worker. But, yes, it is possible.

Yes it's possible, but it costs a lot of money and takes a lot of time. It's better just to refer to eachother as brother and not rely on paperwork and signatures to make your friendship truly official.