Source: immigration record supplied by BB of a John Brewster arriving in Philly, aged 70, in 1826, along with a Charles Brewster, aged 13 = DoB of 1813.
DB: The John Bruster who died in Philadelphia in 1829 was buried at the FRP church, which I assume is the First Reformed Prebyterian.
BB: Using the Philadelphia City Directories as a guideline (and they start back in 1791) the ONLY Brewster/Bruster who is even likely to be the uncle of Charles of Iowa is Charles Brewster who appears in 1820 PCD. Before that there are NO Brewsters except for 3 who are shipmasters (James, Henry and Samuel), various widows, and in 1816/1817 a J. E. Brewster, merchant for only 2 years. A Jonathan Brewster appears in 1817 -1819 and then there is Charles who is there for a very long time from 1820-1850.
So, I would say that this Charles Brewster is the uncle of young Charles and the son of John Brewster who escorted young Charles to America. He probably came shortly before 1820. The fact that they are all recorded in some way or another at the 1st Reformed Presbyterian Church indicates they all came from that Macosquin area of Seceders.
We just need to hope the Iowa newspaper story is correct about Charles coming with his grandfather to live with an uncle. I see no reason why it wouldn't be especially since there is actually a Charles B living in Philadelphia when young Charles arrives.
The only way I can see that Charles Brewster of the gravestone is the same as the Iowa Charles is if 3 of those siblings(Anne, James and Jane) are not in fact his siblings living in Iowa but his cousins. The ages are quite a bit later that Charles and the names are more likely to be first children names than later children names. However, Jane, Charles and Anne named first or second daughters Martha!! That should indicate their mother was a Martha.