Ahh, I suspected that but wasn't sure if that's what you were trying to say.
In English, "everyone/everybody" is treated the same way as "someone/somebody" - it conjugates like a third-person singular (he/she/it), but does not use any articles (I think - I'm a native speaker so I may not understand some grammar rules properly).
So you'd say "Everyone is at home" - not "are".
Honestly, this is quite strange, because in almost all situations the word refers to more than one person, but sometimes natives use this grammar quirk for comic effect (e.g if there's only one other person at a party apart from you and your wife, you might turn to her and say "well, I'll go and say hello to everyone!").
The only advice I have to understand this weird language is to keep practicing - be it through Duolingo, reading or talking with English speakers online. Every English grammar rule has too many exceptions to be explained with logic.
The reason that English treats these as singular is because it is a single group.
I don't think so. I think you need to specify "all" more. "All my sisters are at home", something like this. I don't think it works for "everybody".
Oh dear-I have mentioned this a long time ago. I translated this as 'everyone is at home' and I was told by ye computer that it should have been 'at a home'. Well, nobody says 'at a home' (unles we mean an institution-type home) and anyway 'w domu' translates everywhere else as 'at home'. I am baffled.