I handle all the CRA reviews for our firm, and T777 expenses is one of the most reviewed categories, so you have to make sure that the T2200 is filled out correctly, and that they worked from home at least 51% of the time. If they are required to pay for anything else besides internet, rent, or utilities, that has to be spelled out in the T2200.
If they aren’t working from home more than 51% or more of the time, they can’t claim home office expenses.