Harry and Draco are related very distantly and only speculatively. It is possible that Harry and Draco share great-grandparents, this would make them distant cousins. However, this evidence is conjectural and taken from one name on the Black family tree; Charles Potter who married Dorea Black, Draco's great-great-aunt and possible grandmother to Harry. The tree does not follow Charles & Dorea any further than that but it is known they had one son, possibly James Potter, Harry's dad. Also all purebloods are related. Sirius Black is Draco's 2nd cousin and he is Harry's godfather. That is all I know. Plus, Harry's niece is Victorie, whose husband is Teddy, whose great-aunt, whose sister is Bellatrix, whose nephew is Draco.