The reason I advised consulting a photo of the original will is precisely so this interpretation might be avoided. It seems clear from the original that Henry Kerley is signing the entire document by placing his signature below it on the right side, while the witnesses all signed on the left side. The transcription makes it seem as though the signed "Henry Kerley" was another witness. Another sample of Henry's signature (aren't we lucky to have two examples of his signature!) can be found on a document of the Incorporation of Lancaster Act, 18 May 1653. A photo of this can be found in The early records of Lancaster, Massachusetts. 1643-1725, by H.S. Nourse, page 24. Although separated by over 50 years his signatures are remarkably similar. Just compare his 'y's with his father's or his brother's.