Please check following blog for details: What is the suggested architecture of ThingWorx High Availability (HA)?
Also check following article: https://support.ptc.com/appserver/cs/view/solution.jsp?n=CS241735
Do let us know if you still have any queries.
Out of curiosity, are you trying to connect two TWX instances to the same PostgreSQL *database* or the same postgresql server? You can have multiple instance of TWX on the same postgresql database server by simply creating multiple databases and configuring TWX appropriately, but you cant share a single database across instances of TWX -- otherwise the entities would overlap. You can offload data storage from a TWX instance to a remote data storage server, however -- see: Federation for details.
Need one clarification on Example Architecture provided in 'ThingWorx 7 High Availability Administrator’s Guide'.
If only one TWX instance will become leader and fully connects to the database. what is the actual purpose of other two TWX instances when not fully connect to database?
How are we attaining Load balancing here?