There are at least two locations where there appear to be stone posts installed in the ground to make a triangle.  These are clearly not hitching posts as there is no hole in the post for the metal anchor used to tie a horse lead to, nor are they located close enough to the house foundation. 

The Higginbothams were Welsh, did they keep some of their Pagan Celtic beliefs? 

One of the most utilized occultic symbols is the triangle.  A triangle with its point downward represents the deity and is called the Deity's Triangle, or the Water Triangle. With one point up, it is called the Earthly Triangle, Pyramid Triangle, or the Fire Triangle. These two definitions of the triangle are standard occult belief.

Triangle of Solomon is the second most important tool for the Conjuring Magician next to the Magical Circle. The Triangle of Solomon is used in conjunction with the Magic Circle. It is to sit outside the Magic Circle just a few feet away.  It is used in the Conjuring of the Demonic or Celestial/Angelic spirits. It is in this Triangle that they will appear and are forced to obey.

The Celtic Triangle Knot or Triquetra Knot is a three-pronged knot may symbolize the Celtic philosophy that everything has 3 distinct yet interlocked levels - physical, mental and spiritual. When the Celts embraced Christainity they used this symbol to represent the Trinity. Inspired by the 9th century illuminated Gospels of Lindisfarne, each triquetra (triangle) is constructed of one line to represented strength and give protection to the wearer.

A mystery?