I have always found these vamps in these serials to work in the opposite to their intentions. So the bhabhi's want Gayatri to be their gulam forever and to make her miserable, so they want to reveal infront of everyone that she is shameless at the party, that Rana saved her from drowning in the river that she is secretly meeting with him etc, she's drinking and following Rana to his bedroom that will put her in a compromising situation then the bhabhi's will make the matter worse and any father will say my daughter has been compromised by you, because remember that drink she takes was sent by Rana also Sethji will say that the drink she took was given by you because you had ill intentions towards my daughter, so that could be the reason he tells the Raja to marry Gayatri.
Also if they have no means of paying him the debt and remember Gayatri is under this superstition of people thinking she has bad luck when her fiance died so no-one is coming forward to marry her. Rana will not pay any attention to such superstitions, perhaps its because to him at the moment he doesn't want to live also.