Different websites into one backend

Hi, i have three websites running.
1. Language a
2. Copy with 2 other languages
3. Copy with other content.

All websites have other target groups and so need other google campaigns etc.
The plugins are used are the same and the theme is also the same. The websites do look similar. I would like to have one backend and manage those sites from one place but keep their different domains. What is the best way to do this? Hope you could give me some advices.