Engagement cancel

I had got engaged with a girl and on the same day of engagement my father died,and they felt sorry for my loss and told that this marriage won't be a good decision...and after my father's death,I was also not interested in it.they used to call me often.and I attended the call sometime.but now they are compelling me to marry her because they wil lose their reputation in society if they call off this marriage.and I have told them that I can't be happy with that girl because whenever I see her face i remember my father and his loss.so this will ruin both of us life.butbthey are not ready to hear it.and they are saying that they will ruin my life and career if this won't happen.her mother is a single mother and they are sc category and I am general.i decided to marry her because of getting empathetic by seeing their situation.but they are using these to points to blackmail me.and they even came to my office and made a problem.they are not understanding that I won't be happy after marriage and I can't make her happy.what can I do in such a situation?