Migrating 2 instances of SSRS to a single 2012 instance

A lot depends on how your reports are managed. If you are using 3rd party applications, you may be able to just republish to a new server. Likewise, if you develop reports using BIDS or Visual Studio with SSDT(-BI), you can republish. SSRS 2012 BIDS/VS Report Designer will migrate to the newer schema when necessary. (You can use the SSRS 2016 designer to publish to an SSRS 2012 server but you will need to set the target server version in the report project properties, build the project, and obtain the RDL files from the appropriate "bin" subdirectory where the build output resides.)

I'll assume that your data sources contain database credentials that are encrypted; that is almost always the case. If the data sources are published as shared sources and there aren't very many of them, you can re-create the shared data sources first, possibly entering the sensitive information by hand, and then republish the reports (making sure not to overwrite existing shared sources). The same should apply to other shared resources, but I can't say that I have worked with those as much (shared datasets, report parts).

If you develop your own reports containing embedded data sources, you might be able to convert them to use shared sources before republishing to the new server.

These reports, data sets, and data source files are really just XML text files. You can download them from existing servers and upload them to a new server. You can modify them using an ordinary text editor, although an XML editor would be preferred and BIDS or Visual Studio offers specialized operations that can save you time.

In my work I have sometimes created VBScript files that can be executed using the RS utility supplied with SSRS. I used to use a utility call RS Scripter which was old and was only available as an exe the last time I looked, but which still worked the last time I tried it. I just Googled it and found plenty of hits so it looks like it is alive and well.

RS Scripter creates VBScript files and batch files that you can customize according to your needs and then execute to publish to a new server. My customizations consisted mainly of adding the password information back in before publishing, and pointing to the right servers and report folders.

I also see something called from Microsoft. I haven't tried that one but it might be worth a look.

Thank you