These stones do not look that heavy but looks can be deceiving. A combined total of 333kg.
According to his account on gordondinnie.com, very few strong men of the day could lift the heavy one (187kg) with both hands. However both stones were lifted and carried the width of the Potarch Bridge (4 metres or so) by Donald Dinnie in 1860 across the River Dee in Potarch, Scotland. They have since been known as the 'Dinnie Stones'.
I was challenged to this yesterday by my friends who said they had a surprise for me. :-)
There were several "be careful, I've seen many men carried off to hospital pulling their backs out" warnings from the locals but I was able to safely deadlift the heaviest stone (twice my bodyweight) to full height for a few repetitions but absolutely no chance of lifting both stones together!
Regardless I am more than happy with my result. :-)