I read about the fire at the city hall. From what i read, the fire didn't destroy any records. Unless there was a second fire that wasn't mentioned on this page.
Anyway, I found a website talking about vital records in Butler, PA and for the time period we are looking for, it said to contact the Register of Wills and I found her e-mail address. So I have an e-mail into her requesting the direction to take for finding death certificates for Augustus and Joseph. And as a side note I also asked about Boggsville Cemetery. Did you ever find any more information out on that?
Judy Moser, Register of Wills Butler County, PA firstname.lastname@example.org