This is strange, besides the 100 pages I have of Warrington MM records, by Cope, I have the sister book to Menallen, by Margaret B. Walmer, "100 Years at Warrington" and "McElwee" is not in the index.
I have a post of Warrington cemetery inscriptions (I should have looked at this first) and I show two McElwee's buried there, Samuel & Joanna, who I'm assuming are husband and wife. Check it out.http://www.interment.net/data/us/pa/york/warrington.htm
The work done by Cope, 1877 and Margeret B. Walmer, 1989 are pretty much the predominant sourses for Warrington MM records.
You do realize that a "family file" is work done by someone, not necessarily a professional researcher, then they contributed the work to York County Heritage Trust.
YCHT does not verify or confirm the accuracy of the work, they just accept it. All material from such a source has to be checked and confirmed.
Have you found the probate file for Charles, ie: will and/or estate file. I have land records for Warrington township and there are several McElwee's including Samuel & Charles. If you're interested I'll scan them and email them to you.