Hello,
Looking at the
definition of postgres_fdw, we notice a comment: "The functionality provided by this module overlaps substantially with the functionality of the older dblink module". It is meant to access a foreign table from PostgreSQL in general, while tdw_fdw appears to be specific to MS SQL Server. Both access data from a PostgreSQL server, while you want to access a PostgreSQL instance from MS SQL Server. To this purpose, you may consider other solutions, for instance
Connecting SQL Server Management Studio to PostgreSQL via ODBC Driver.
This discussion group is oriented more towards general opinions, trends, and issues of general nature touching App Engine and Cloud SQL. For coding and programming architecture, as well as setting up MySQL instances, you may be better served in dedicated forums such as stackoverflow, where experienced programmers are within reach and ready to help.