ituneslibrary-management
My wife and I both have iOS devices (some iPods, an iPhone, soon an iPad), which means that both our iTunes libraries have not only music, but also apps, podcasts, iTunes U stuff, etc.
How could we manage to share just the music in one single location, and still keep our apps/podcasts/etc separated from each other?
Home sharing should allow you to see each other's libraries over your home network, and drag apps from your wife's onto yours and vice versa. You can definitely do this despite having two accounts - my wife and I have a similar problem. You may have to enter both passwords from time to time to authorize purchases, though.
I found some help setting this up from "Activating Home Sharing in iTunes".
I believe you can also sort hers by "items I don't have" so you can see what she might have bought of interest to you, although I'm not sure you can automatically sync them.
This SuperUser question seems to suggest that merging two accounts is not an option:
Can I merge 2 iTunes Store accounts?
Simple.
I haven't tested it, but WiFI sync might also be available on the PC side of iTunes. Good Luck! Let us know how you fare...
Best Answer
Would iTunes Home Sharing work for you?
Basically, one of you would have all your music, but every device would have access to it.