Lisa - Some researchers indicate that Nicholas Heavner's father, Wilhelm Haffner (William Heavner), was killed at the Seybert's fort massacre.
I have seen no supporting citations nor any independent proof of that though. No complete list of names of the victims of that massacre has ever been discovered so proving someone was present can involve a great deal of work.
A Kile-Coil-Kyle family researcher posted an excellent research piece on-line about one of Nicholas Heavner's daughters, Maria Johanna Heavner (later Mrs. George Coil) who was taken captive at the massacre but, to my knowledge, those are the only two Heavners who are said to have been at the massacre.
Perhaps a Heavner or Coil researcher (or someone else who has worked the massacre) can add to this for you.