The density of water is 1,000 kg/m³.

The density limestone is around 2,500 kg/m³ (it can actually go down to around 2,100 kb/m³).

This means that you'd need to displace more than 2 to 2.5 times the volume of water in order to float a limestone block. Keep in mind that volume goes up (roughly) as a cube of the increase in linear dimension, so the difference won't be quite as dramatic as it first seems, but that's still a lot of flotation required. Certainly much larger than the floats shown in the video.

The animal-skin bladder theory is particularly problematic, because the volumetric efficiency of spheroid animal-skin bladder floats isn't particularly good. Water would fill in the space between bladders, requiring much larger float assemblies than if they were able to construct larger, single-chamber bladders. The video depicts float assemblies that aren't even as large as the blocks they were transporting. I found that rather disappointing for an engineering-driven theory.