Is there still possibility to sign in with the Facebook account?
I think so but I just want to make sure. And there isn´t possibility to add community feed/app to Facebook page?
View Facebook Authentication guide for more information about how Lithium's Facebook Authentication work on community.
If you'd like to get a quick start and get up and running with creating your first app in App Creator, please see this article.
Your first link and there says:
Availability Update: The Lithium's Facebook Integrations for Communities (also known as LevelUp) is no longer available for purchase.