DNA testing is now required to prove relationships. DNA cannot be faked. Perhaps hacking into a DNA labs database and changing out information might be possible to someone really skilled but the chances of that happening are quite remote and though not impossible I would say highly unlikely.
For a while Immigration was only accepting DNA from a parent or grandparent as acceptable DNA proof of relationship but as of April 17, 2018 sibling testing for immigration has become an acceptable form of proof as well since both grandparents and siblings each contribute the same amount of matching DNA which is 25%.