2 Jerusalems - Gal 4

[Deleted User]

Hello everyone,
Gal 4:25-26 mentions 2 Jerusalems => (1) Jerusalem which now is, (2) Jerusalem which is above.

Gal 4,25-26 (AV)
25 For this Agar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children.
26 But Jerusalem which is above is free, which is the mother of us all.

To whom or what do these expressions refer? Here again we also see a NOW ("which now is" - now when? then now? or in our day and time now?
Does the mention of "is in bondage with her children" provide understanding to answer the question about who or what is being referred? what is emphasized by the expression "mother of us all"? who are the "us" in this expression?