Posted: 15/08/2014 at 06:31
I once had a similar problem - tall sanseveria leaves bending in the middle and flopping over in a previously very healthy plant.
I eventually realised what the problem was - we'd moved house and the window sill where the plant now lived no longer received as much bright sunlight as the plant was used to. The leaves grew taller searching for the sunlight and eventually couldn't support their own height.
I cut off the flopping leaves at the base and moved the plant into a sunnier spot. When new leaves grew they were shorter and sturdier.
However, my plants didn't have problems at the roots, as yours do. I suspect that planting them too deep has caused this.
I would re-pot in a really free-draining compost (at least one third vermiculite or similar), and make sure that it's not planted too deep. Place in a really well-lit windowsill, water once and then not again until the compost feels really dry an inch below the surface.
I hope that helps - good luck