No. Male relatives on the same paternal line usually share the same Y profile, so a match points to a family line.
It can sometimes be recovered from hair shafts, old bones and teeth when standard DNA testing fails because of degradation.
People on the same maternal line, such as a mother, her children and maternal siblings, usually share the same sequence.
Generally no. They are often based on how often a profile appears in a database and are much weaker.
Yes. A difference can be strong evidence against a paternal or maternal line, subject to the laboratory's conclusions and quality checks.