Remove Legend items, move legends

I have 3 plots and I would:
1) I would create a Legend inside the plot
2) Take the legend only for 2 of them.

Now, to make the legend inside to plot, i use ExternalPostion, but I don't now I to move it inside the plot.
Moreover, to remove a curve form the legend I used legend->remove(myPlot), where myPlot is the plot I don't want inside the legend.

But nothing works!