AbidSiddiqui welcome to Flyertalk and especially to the QR forum.
I assume that two passengers are on one PNR and one passenger on the second PNR.
How many rooms do you need to reserve?
If it is three single rooms then you need to apply three times, once for each ticket number.
If a double and a single then you need to apply twice once with a ticket number from the two person PNR, which number you use does not matter, and once for the single person PNR.