the ice sheets contain 2/3s of the water on earth?????????????
2/3 of the fresh water.
2/3rds of the fresh water, not the whole shebang.
If the parts of Antarctica which are currently above sealevel were to lose their ice (a good bit of the Antarctic ice is submerged as a consequence of having pushed down the elevation via the massive weight, and oozing off into the sea while still connected, that kind of thing), the surface area involved isn’t much compared to the 70+percent of the Earth’s surface that are the oceans and seas. So, the total sealevel rise from such an event would raise sealevels perhaps 40 feet, maybe a bit more.
To put this into perspective, during the most recent glaciation, the sealevel fell hundreds of feet (as much as 800 in the Bering Strait for example) and the Gobi Desert of today was the bed of an inland sea.