We have to Invision forums that we would like to merge into one. Is this possible to merge users, admins, and threads into another forum account?

Thank you for the help.

Yes

Just use the converter to import Forum A into Forum B.  

Before you do, make sure you take a backup of all files and databases.  You can also perform on a test installation.  

If you're cloud, contact Support to assist you.  

Thank you Joel for your help.