It is settled science that ice displaces more water than the water that makes up the ice. So when all the ice in the water melts, what happens?
Sea levels drop!
Ice is less dense, but because it is less dense, some of the ice is above the water level.
So when ice in water melts, the sea level remains exactly the same.
You can check this yourself by putting some ice in a glass of water and marking the water level before and after the ice melts.