Security seems to me a poor place to enforce baggage weight restrictions.
One problem is that one could have different weight allowances depending on the airline.
The weight limits for carry-on baggage are clearly shown on the tickets - 7Kg in OZ.
Ensure the baggage (size and weight) are within limits at the boarding gate.
If the SLF cannot stick within the limits for the baggage, leave the overweight/oversize baggage behind to travel as freight on the next service. Been there, done that.
Once it happens a few times, "social media" will spread the word quickly.