Hello Shaun.
Yes. Quite alot of progress but just a few missing links. You had me going with Frank J Prendergast, wondered where he had appeared from but I think you mean Frank J Davenport.
Disapppointing not to see a marriage for him and Sarah/Saddie - it would have confirmed a surname for her. We know she was listed as an Armstrong but 1910 said adopted child - it could be that she was'nt legally adopted and may go under a different surname !! (Just a thought anyway - these things were quite expensive then !!)
Apart from that, we still have a missing death record for John H Austin and a marriage for Isabel to Daniel Simpson. (Although you have a time frame for those)
I wonder if you could get an RAOGK in Philadelphia to check for an obituary for John H Austin, if it was an accident of some sort you would think something would be in the newspapers.
I will put a link on to see if you can find anyone on the list that could help. Always worth an e-mail !!!
http://www.raogk.org/pennsylv5.htm