merging multiple iTunes accounts in my home to one for four different devices we now own

I am having a major $%#@^ issue here. I started out with one iMAC six years ago and have now progressed to one iMAC, one MacBookPro, one iPAD, and one iphone (soon to be two). The issue is is that my wife and I created two different itunes accounts. At one point we were even told we had to create an .me account so we did. So that brings us up to three accounts on itunes for the same household. We would like to merge all of these into one account so that purchased items on the iMAC may be downloaded between all of our devices. Any suggestions?? genius bar at the apple store was useless. .

Thank you in advance.