In the above mentioned case, Nikah will be valid if the groom had met the conditions of Kafaa'at or else the parents will have the right to nullify the marriage.
The conditions which are to be present in the two witnesses are. Eg they are Muslim, they are of a sound mind, and they hear the vows being exchanged, they are not slaves, they are either two men present or two ladies and one man. (Al-Hidaayah, Kitabun Nikah)
In the contemporary era, the fact that they are not slaves will not apply in many incidents.
However, Islam advises to keep close links with our families, and the parents duas are very important, therefore do try to bring your parents round to accepting him into your family, and do not cut off relations with them.
Inshallah may Allah make things easy for you with you parents, Ameen.