See http://help.geni.com/forums/367927-Merging
More simply:
- In tree view, select "move" one of the duplicates, the node will hang to the right on a lightbox
- open a new window to the same / duplicate tree
- wait for the lightbox to load, then select it and drop on the duplicate
- you will be asked - same, brother, son ... Select same.
- this opens a detail screen to compare field by field
- OK button
Be sure & resolve any data conflicts (date discrepancies, name case differences, etc). Easier to do this at merge time.
Post back if any difficulties.