This is the 8583rd most frequent Japanese word.
揃う
To be complete, gathered, or in order.
The word '揃って' indicates that all members are together and complete in attendance.
皆が揃って会議に出席しました。
Everyone was present at the meeting.
In this sentence, '揃っている' refers to the completeness of required documents.
必要な書類が揃っていますか？
Do you have all the necessary documents?
Here, '揃った' implies that all members have assembled or come together.