How to daily copy selected data from MySQL and PostgreSQL servers to another PostgreSQL server
What you are looking for is called ETL (extract transform load) tool 
https://en.wikipedia.org/wiki/Extract%2C_transform%2C_load

There is no FREE/open source pre-built tool that exist to do what you want when moving data from different databases  that I am aware of.  I have used the paid for ETL tools they just speed up the process coding/typing time.  The computer generated scripts  always require tweaking to get to work and speed them up.

here is list  i found... (no idea how valid this review is,  i do not use such tools)
https://suyati.com/blog/top-10-etl-tools-salesforce-data-migration/

What you have to do is write scripts that update the tables in sequence you want. 

This script can be python, perl, or some other script that runs and moves the data from one server to another.  

Another option is use FDW on the PG 11 server to copy the data from the MySQL and PG 9.6 server.  Using FDW means it can be done in pure SQL using simple Updates and Inserts.
https://www.postgresql.org/docs/current/postgres-fdw.html
https://wiki.postgresql.org/wiki/Foreign_data_wrappers

To execute the  SQL script use PG Agent for Perl/Pytho/other script language use cron Job.