sahirs past my guess

might be that sahirs mother was alviras best friend and had lots of money. Sahirs mother may have asked the chaudhary family( nee alvira) to be the legal guardian of sahir hence the gratitude and indebtedness he shows towards alvira and calls her ammi and thats why he calls zaki his brother. And maybe his parents died an unnatural death and alvira may have forcefully taken the sign of sahirs parents of nh. Remember that alvira and her family were not well off and so nausheen gave her support. It may have happened that when sahir became an adult she saw the opportunity of living in such a big house going from her hand and so asked sahir to marry zeenat. After marriage alvira told zeenat to get sahirs sign for the property papers. It might also be that zeenat had may relationship with men and that is whg he does not trust women. But zeenat could not get his sign and had an accident which resulted in her being in coma and beginning of saiyyara which is sahirs and a rightful owner of nh as well