First off, welcome
Hmm a confusing question...
I know for sure it doens't matter what sizes the RAM is to run compability in your computer, but for Dual Channel, this is the case I believe, and also, I believe, but I'm not completly sure, that you need 2 compatble modules for this to work and not 4.
I'm not sure about the 1 sided RAM module to the dual sided one though I'm afraid
I'm sure someone can help you out better than me