I felt I had cheated a bit when I bagged Longknowe Hill NE Top as it was just down and up a little saddle from Longknowe Hill. I'm not sure why they aren't just part of the same hill, it must have a high enough prominence to be a classed as a hill in its own right.
Quickest route is to park in the Hethpool car park, ascend White Hill and then keep heading west until you get to the trees at the foot of Haddon Hill. Then head up Longknowe Hill and then a quick down and up to the top of Longknowe Hill NE Top.
Follow the route above or find it on OS Maps. Just under 5km and 370m of ascent.
To complete the trilogy in this little range, keep heading on to Kilham Hill.