If I understand your question correctly, you are trying to have a different frequency offset for each IQ Dataset from the center frequency.
If this is the case, to get a different frequency offset for each IQ Data set , perform corresponding frequency translation on the IQ Data Set.To Perform frequency translation, the trick is to multiply the IQ Data by exp(-j*2*pi*f0*t) where f0 is the frequency offset , t is the time vector. Note the mulltiplication here will be dot product. You can perform this multiplication for each dataset by having frequency offsets and then add all the IQ Data.
I am attaching an example in LV 8.2 which will demonstrate this trick. This VI demonstrates generating complex sine tone and performing a frequency offset defined by the user. Displayed spectrum shows frequency translation in frequency domain.
You can play with frequency shift slider on the front panel and notice how frequency translates.
Yes, You got it.
You just have to add the arrays point by point. LabVIEW's addition is polymorphic in nature. If two arrays are given as input to the addition function in LabVIEW, they get added point by point.