Thanks much, Darlene.
It appears that your post put me on the track I was looking for.I will probably have to plow a lot of ground that others in the forum have been over many times, but I'm up for that.
As to separating Isabella's children from Roena's, I am not sure how to do that just yet at least, but here is what I have obtained from the 1850, 1860 and 1880 census record for Helen township, for the household of John and Roena.
John Callihan b. about 1784, m. Roena (or Lydia?) (last name not found).
P. 413 of the 1850 census for Helen Township, Clarion County, Pennsylvania lists John Callihan (farmer, age 66), Roena Callihan (age 56), and Robert Callihan (age 16). Apparently the 6-year old was John’s son and my great-grandfather, Robert B. Callihan, who later married Nancy K. Piper and moved to Bergen, Minnesota.
Also listed together in this 1850 census are John H. (farmer, age 27) and Nancy A (age 25) and Mary A. (Age 3) Callihan, who may well have been son, daughter-in-law and granddaughter of John and Roena.In such case John H would be brother to Robert B. Callihan.
Also listed in the 1850 census are George (farmer, age 36), Rebecca (age 34), Sarah (age 11), Harvey (age 10), Robert (age 8), Rebecca (age 6), Elizabeth (age 4) and Andrew (age 1) Callihan; these are also of the age that could be that of children and grandchildren of John and Roena Callihan.
The 1860 Clarion County census for Helen Township, p. 183, lists the family of John (farmer, age listed as 66) Roena (age 64), George (farmer, age 46), Rebecca (age 44), Harvey (farmer, age 21), Robert (farmer, age 18), Rebecca (age 15), Elizabeth (age 12), Andrew (age 10), George H. (age 5) and Allen M. (age 2) .This listing suggests that they were living there at least from the 1834 birth of their first child until the 1860 census, i.e. for 26 years or more. The entry I transcribed from this census record for John’s age is in error - whether mine or the record's error, I don't know--; he would have been 76 in 1860.Some discrepancy appears in Roena’s age as well; if 56 in 1850 she would have been 66 in 1860.
The 1880 Highland Township, Clarion County census lists, under the household of William Whitehill, Andrew Callihan (age 36) and wife Mary Callihan (age 26, b. PA, parents b. France).It appears likely that this Andrew was the 1-yr-old son of George Callihan, shown in the 1850 census.
Also listed in this 1880 census is the family of George (age 66) and Rebecca (age 64) including widowed daughter Rebecca (age 35), son George (age 24), Mary (age 19), grandson Harvey C. (age 10), granddaughters Alice C (age 8), and Mary E. (age 7).
I have reliable information about the Callihan lineage from Robert B. Callihan through his son Lindley Robert, his son Harold Gardner (my father), and of course, myself and children.If you're interested, I'll send those data.