Linking multisites

I want to make real estate multilingual website (English-Arabic) so I will use WP multisite feature and I will install the same theme for both sites each theme with the proper translation and styles.
But this is my first time to use this feature so I have some question.

What I want to know about:
How can I link the sites so that:
1- when I enter a new property in the English site it is automatically inserted in the Arabic site?
2- Any user who registers in the English site is also registered in the Arabic one and viceversa.

I hope that you’ve got it 🙂
Thanks in advance