Momentum Multiply useless to me

I'm a premium Momentum Multiply member. Since only I have multiply and my family does not, I want to book for a single adult (Family room) and the pay the additional cost at the hotel for my spouse and child. So the Momentum travel desk's response is "Regrettably we cannot book a family room for 1 adult, we can only assist with a standard room." So what they are telling me that although I have the money to pay for a family room, I cannot book it because I'm a single adult. Do yourself a favour a do not get Momentum Multiply. There is always a long story it seems!