How many inches do the pegs stick up?

If you have at least 2 or 3 inches, I'd scrape enough earth from immediately around the pegs so there's an indentation, then water the indentations very well. After that, whack the pins on 4 sides with a sledge hammer. If they don't wiggle, add more water.

I'm familiar with re-bar (and lead pipe) used to hold railroad ties and landscape timbers. Do your pins have the corrugated sides of re-bar? If not, how wide are they?

Are there any trees or shrubs that might have roots holding on to the pins?

I think it goes something like this: take 5 foot long piece of 4" x 2" and cut a notch a foot from one end to accommodate the pegs. Slide this notch over the peg and rest the closest end of the 4" x 2" on the ground then lever up from the other end.