just bleach everything but the sand, wash them really good, and allow them to dry (in the sun if possible). The sodium hydroxide in bleach, which is what cleans and kills everything, dissipates once fully dry and becomes harmless. Once dry you can fill the tank with everything in it and quadruple dose with some water conditioner and let soak for 48 hours to help remove any chlorine that might have stayed behind from the bleach.
if that sounds too complicated, then vinegar will also work but will take alot more scrubbing and cleaning to make sure any bacteria that grew from the stagnant water is gone.
the sand may be hard to clean, but you can always just boil it for a few hours to make sure its clean, that would be easiest.