“When Parents Don’t Support a Shidduch…”
I know this is extreme, but if you are 100% certain that your choice of a shidduch is correct (through objectively looking at the situation, discussing with rabbeim, teachers or whoever it is you turn to in life), then I say go ahead with the shidduch, but be prepared to be without parental support. I use the word support with all its connotations.
Be open and honest with the other side of the shidduch and let them know how your parents feel. It is not fair (and is likely against halacha, but obviously not issuing a psak here) to the other side and quite dishonest to allow them to enter into a shidduch not knowing this basic fact.