On PC#1--> make sure it uploads (or synchronizes) the archive folder to a cloud (Dropbox), or for example sync it with SkyDrive for Windows (this was formerly called Microsoft Mesh) to a folder called 'C:/HMArchive2-PC1
On PC#2 add this C:/HMArchive2-PC1 as an auto import folder
On PC#2 --> make sure it uploads (or synchronizes) the archive folder to a cloud (Dropbox), or for example sync it with SkyDrive for Windows (this was formerly called Microsoft Mesh) to a folder called 'C:/HMArchive2-PC2
On PC#1 add this C:/HMArchive2-PC2 as an auto import folder
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Alternatively just use your external drive.... and once a week copy the C:/HM2Archive of both computers to the external drive.
Then on PC#1--> import PC#2's archive folder and vice versa.