I would like to write my post in one of the my 3 blogs and the same post will be published in the other two blogs.
How can I do that?
You can hook on
Alternative is you search for a plugin, there doing this; like Multi Post. I don't know if is the right and a good plugin. I had use the search on www.
You can use the WordPress XMLRPC API. http://codex.wordpress.org/XML-RPC_WordPress_API
Alternatively, take a look at the following plugin: https://wordpress.org/plugins/syndicate-out/installation/