Good evening, I would say that DNA is enough to link all people to the very first humans. But the only issue would be that you did not have either two first humans DNA to form a comparison. That would be the best and most accurate way to see human genes and how they all connect and stream from these two people.
Another thing is that Adam and Eve would have to be alive in order to attest to the fact or have some record left directly from the two of them that would prove authenticity. A big question surrounding the existence of Adam and Eve would be because the Bible tells us that the wages sin pay is death, Romans 6:23. In light of this Bible passage can humans accept that the two first humans were judged and naturally died. Did it ever occur to you that without imperfection people would live eternally? Well only God can answer questions of that nature as for who we are and where we came from. Do you believe that God is living?