All users must upgrade to the same version of Act! in order to continue sharing the database. Users who have not upgraded will not be able to access the database. Once upgraded on the server, remote database and Offline Client users who have not upgraded will not be able to synchronize. It is strongly recommended that remote database and Offline Client users do not attempt to synchronize until after the main database and all remote databases or Offline Clients are upgraded and converted to the new version.
Also, v19 (or later) should work with x64 office. No need for v22 for that. But you should reinstall Act! after uninstalling and reinstalling Office as x64... So it's not a bad idea to do the upgrade at the same time