I agree with you, the date of death on the will is the date of death on the son Neill-178. I also looked at the names in the will some of them are repeats, but gilbreath is only on the 2nd william and is mentioned as son. To further verify, you could identify who the daughters of the 2nd William were supposed to have married.
I also noted that some of the children on William the 2nd, were born before his marriage, which should be looked at.