Hi Kamal,
I don't quite understand the question, but I'll try to answer below. If you have schematics of what they want, it might be easier.
First of all, they can take a look at the following app note for guidance:
http://www.ti.com/lit/an/slaa399/slaa399.pdf
If a 2:1 transformer is used with 50 ohms to ground on each leg and a 50 ohm load at the output of the transformer then the signal swing at the 50 ohm load will be 0.707 Vpp (1 Vpp differentially at the DAC output). This doesn't meet their +/- 1 Vpp requirement. So perhaps I don't understand the circuit they are describing.
Regards,
Matt Guibord