Found this thread:why the oath invitation doesn't say how many guests can I bring? can I bring two?
https://www.canadavisa.com/canada-immigration-discussion-board/threads/how-many-guests-were-you-allowed-to-bring-at-the-oath-ceremony
TL;DR version: no limit as long as hall capacity allows (also if there is a limit, it is usually stated on the invite). If it's full, they will have to wait outside the ceremony room. Apparently, there is a TV they can watch the oath ceremony on live.
I think common courtesy dictates 1 or 2 guests at the most. I'd stick with 1.