I have listed the following children for Jacob and Prudence: David Tutterow (1809), Jesse (1811), George (1812), Bettie (1814), Tom (1816), William (1819), Hiram (1821). I'm only assuming that all of these are children of Jacob.

I think you may be correct that this David Casey is the father of two children by his wife's sister.

I have a little more info posted here:
http://freepages.genealogy.rootsweb.ancestry.com/~soneal/CAS...

and here:
http://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi?op=GET&d...

that may be of interest to you