Actually you can quote multiple users in one post but you have copy the author's link and his/her message when you press quote button (there's no button to press that will copy the author's link and message though).
I think it would be a great feature to this forum if people could quote multiple people in a post with the click of a button.
I'd love to have it featured in this forum, when you want to quote multiple person in one post you just have to press a button.
It seems that it's possible if "Quick Reply" option in Settings is enabled: it that case the "Quote" button adds quotes to one post in sequence, not sends you to another page.
It's still possible even though you use another program like notepad or html editor something like that. Quote button will help you to quote multiple people in one post.
Recently, I had to quote two people who posted before me in two separate posts.
Since you found an answer for your question I can only add little information. Learning BBCode would also help you with your post, I suppose you knew BBCode.