Antarctica doesn't have to all melt to have a significant effect. Just a couple grounded ice shelves break up, and we have a couple of meters of sea level rise.
As only something over 40% of Anarctica has ice shelves and only about 1/9th of those extend above the ocean surface, they all could melt without causing significantl rise in the ocean levels though it could cause some desalinization which could have other effects. If the anarctic ice that is grounded should melt, that would be a real problem, but as already posted, there is little or no chance of that happening in a future we need to worry about.
That is not true.
If the permafrost melts and releases all the methane, we will have a lot to worry about.