So here's what I have found so far. William Fiske married Phanulia Wight bef 1826, most likely in Masachusetts but not for certain. While living in Dorchester, Mass they had the following children: Harriet Fiske b. 19 Jan 1826 Caroline Fiske b. 11 Mar 1828 William Joshua Fiske b. 15 Mar 1830 Hiram Thaddeus Fiske b. 18 Dec 1831 d. 6 Mar 1910 in Charlestown. (Obtained mother's maiden name "WIGHT" from death record.) Children born in Charlestown: Unknown Fiske b. abt Dec 1840 d. 24 Jul 1841 in Charlestown. Charles Henry Fiske b. 19 Jul 1845 d. 04 Aug 1846 in Charlestown. Charles Henry Fiske b. 25 Aug 1847 d. aft 1860 possibly Charlestown.
Phanulia, Pamelia, Fannelia... however you want to say it, died 20 Sep 1866 in Charlestown. Her parents were listed as unknown in the death record index, which makes me think either her husband William was already dead and no one else knew, or she died alone. The death record index does say she was born in Stockbridge, Ma.
I will continue to search for this family but I wanted to give you what I have been able to find so far.
As for the chance that the William Fiske family of Dorchester is not the same as the one in Charlestown, I very much doubt it. Hiram's death record, he being from the family from Dorchester, lists his mother's maiden name as Wight and in the 1860 census for William and "Phanlia" Fiske of Charlestown is an elderly woman aged 82 named Mary White.
I am fairly certain that this is the right track. As I always say, you really can't be 100% sure until you get the records in hand.