Help with db scenario

Hi, I would like to request some help from the community understanding what
would be the best solution for my problem.

I have been presented with the following db scenario:

(Using PostgreSQL 9.4)

Customer A has DB A;
Customer B has DB B;
Customer C has DB C;

All the databases should "see" changes between them. For example: DB A
should be updated with changes in DB B and DB C, DB B should be updated
with changes in DB A and DB C, etc..

All the databases are hosted in windows servers and should be updated as
quick as possible. Also the servers are connected via Internet and can at
times be disconnected (not accessible).

- What would be my best choices for data replication between these
databases? Windows solutions would be preferable but Linux solutions are
not excluded.
- What would be your main advice regarding a complex scenario like this?
What should I be looking for?

Any help and hints are appreciated.

Thank you in advance,

*Ricardo Oliveira*