If you follow this link, on the right side is a little gear and if you hit the down arrow, you can download the pdf version of the "History of Littleton, NH"
It seems to have the same info you have. I was able to find a second marriage for William Fisk Jr., which you did not mention, to a Catherine Chase but it says her father was surnamed Moulton and that this was her second marriage also. So I assume her name, when they married on 2 July 1881 in Whitefield, Coos, New Hampshire, was actually Catherine (Moulton) Chase.
William Sr. is referenced several times in several publications but none lists his ancestry. At 100 years old when he died, I will be amazed if there is no mention of his parents in his obituary, if one can be found.
I'll keep digging and let you know if I can find anything more on this family, especially Wm. Fisk Sr.