Multilingual web site

Hello, I’m in the process of building the website using the Healthflex Medical Health Wordpress theme, which I need in 4 languages: English, Greek, Spanish and French.
My questions are:
Is Healthflex compatible with Polylang, or just with WPML?
I have been customizing the child theme, and working on the English version of the site. Should I have installed WPML first?
Should I install it on the child or the original theme?
4) Finally, a question unrelated to the multilingual issue: I am using the Top Bar (and the “emergency line…”) that appear on the home page, but I can’t see them on devices. How can I make them show also on devices?

Thanks a lot for your precious help.