I don't think much of the 'pay for' sites, either, and have none.....there's too much to check out before one has to resort to paying for info!
Okay, how do you know Eli was born in Chester County in 1725?...the actual documentation for the birth....that would be good to know as a clue as to where to be looking. Ditto for the marriage of Charles and Katharine in 1727....the actual proof....again, a good clue. Let me know.
Be sure to do a patriot search for Charles on the DAR online site.....who knows? You might get lucky. Have you ever looked in the blue DAR Index that you find at the library, to see if anyone had joined with either Charles or Eli as their Vet? I'd sure do that, as you can order a set of the papers that have, named, the proofs the woman used when she joined, and these can be a tremenous help. If you find Charles in there, be sure to ask for the papers of any woman who joined through Charles's son, Eli.