Had to read this twice before getting the grammar. `Er' is rarely met in Duolingo, I think that was the problem!
Yes, here you are urging more than one person to stay at home. Er = pronoun for the 2nd person plural. I don't know if it would be possible to say in English "Keep yourselves at home!" ???
I have the same question? Which one is more idiomatic? Or is there a certain context under which they are to be used?
It appears to be a reflexive verb, hålla sig. At least, I haven't found examples yet on DL where the reflexive pronoun isn't required.
Would this be something like "hold yourselves at home" (making a too literal translation, of course)?