How old are you ? what are you studying?, First let us know, how come you got engaged to that girl one year back, what makes you to decide for that [engagement]. Now why do you want to postpone the marriage, If you come across any strong reasons for postponing the marriage, then there is way. You could have think this long back. But you are spoiling that girl's image in society for your gaining. OK you are asking 6 months time for marriage, but your parents are not listening, may be the marriage date is already fixed after the engagement, all the relatives/friends know this, this is their family reputation. Why cant you marry that girl and let her be there in her parents house for one year ?
Better Wait for Experts Advise