I read of something called "structuring" - like, if one family member say has 5k and the other 6k on them the CBSA would consider it "structuring" the amount as to not report it as 11k. My understanding from the previous answers would be that even in this case, while none goes over 10k, you still have to check that box because the total per family is 11k so it's beyond the threshold.
I was curios if someone was in that situation and what the officer did after or ask them to do after.