Yes, steel fence posts are difficult to remove. This is especially true if they are set in concrete. It may be necessary to rent a farm jack from a tool to remove them.
There are several chemicals available that will kill poison ivy. Check with your local lawn and garden store to see what they recommend. Ivy is a woody stem plant and normal weed killer like 2-4-D...
Some people would say that the correct answer is twelve. However, if you include the FIRST square fence post that is used to give placement references to the four sides of three posts on each side...