BJJ:
A. There is no inyan of kibbud av regarding who you marry. You have no mitzva to listen even if they threaten to disown you.
B. Usually, when 20 year olds say “I don’t need to ask, I know the answer”, it is because they are afraid to ask. I have no idea why you would be afraid to ask here.
C. It is odd that you are sure your father would disapprove so strongly, when you cannot even state a reason why you think it is objectionable, beyond a vague “not tznius”.