It is possible to merge two family tree projects in Family Tree Builder.
In order to merge trees one of them will have to be exported to GEDCOM file format. Any time you export or import a GEDCOM file of your tree any photo in the tree must be replaced manually.
IF YOU EDIT YOUR FAMILY TREE ONLINE YOU MUST FIRST DOWNLOAD FAMILY TREE BUILDER AND EXPORT A GEDCOM FILE OF YOUR TREE FROM YOUR FAMILY SITE (FAMILY TREE > MANAGE TREES PAGE).
To do a merge, export one project into a GEDCOM file.
Then open the other project, and choose import GEDCOM. You will be asked if you would like to close the project that is now open you should click on yes.
In one of the steps of the wizard you will be faced with the question of whether to import the GEDCOM into a new project, or into the last project. Chose the last project, and they will be merged. See below the option you need to pick in ‘Import GEDCOM’ in order to get the merge working in Family Tree Builder.
Before doing this, please backup both of your projects (using File > Back up project) so that if the merging isn’t to your liking, you can always revert back to your previous trees.
Find and delete duplicates in the merged tree:
Please note that merging the two trees will not automatically merge people who appear in both trees. This means that you will need to detect duplicates manually. This can be done by sorting alphabetically, and then deleting them. Another option is using the “check for duplicates tool” by going to Tools > Check for duplicates.