Hard is probably a relative word. Consider that just over 100 years ago, when there were no power tools or power sources to operate them, furniture making had been in existence for over 4000 years. Look at some fine examples of 400 year old furniture, crafted with no more than skill and hand tools.
It's more tedious, if anything, and takes a finer set of skills to create a finished product, but HARD might only be defined by the craftsman.
Certainly if you lived in a Mill, and had a water wheel attached, belts were run and "power" tools were used.
Your brother might research furniture making techniques, before electricity, and tools used. One great example of a TOOL before electricty, is the function of the pedal/pump type sewing machine. Similar methods were, and can be applied to some carpentry tools.
Obviously it was a Mallet/ chisels/ hand saws, and scrape/draw blades/ some manner of smoothing, before sand paper was produced, etc.
Just my two "sense"