Okay... we may be getting somewhere...
But before I do... If Foster Jones' wife died before 1910, then he should be enumerated as widowed, not single, but census takers weren't perfect. So we'll set that aside for the moment. Also note: There are also many other Jones' on the same census page in that 1910 census.
My next question is: If Hazel Jones was sister to Harry, and by implication of having raised him, OLDER than Harry, then where was she in 1910? Well, I found her, also in Burrell, Indiana Co., PA), enumerated as age 6 (mm... younger than Harry by a year), grand-daughter of Delilah Myers on Strangford Road! Delilah is widowed, age 65 [b 1845], having had 7 births, 4 of whom were alive in 1910. Delilah was born in PA of PA-born parents. So... that's likely the mother of your Margaret Myers Jones, and raising one of her dead daughter's children.
I do not find Delilah b 1845 easily in 1900. The closest is a Delila Myers, b Jul 1850 in Tyrone, Adams Co., PA, married to David B. Myers, grain merchant, with children Edith E (1879), Laura B. (1882), Grover (1883) and Elda R (1888). But what looks good about this is that Delila is listed as having had 7 children, 6 of which were living in 1900. The 7 matches the 7 births of 1910. This implies that if Margaret was her daughter that Margaret was already married by 1900.
Now... let's go look for Foster Jones in 1900. We find a likely candidate for the Foster Jones of 1910 above, in Burrell, Indiana Co., PA, born Dec 1869, married to a "Jenny" born June 1875. They've been married 2 years, and already have a child, Stella, b Apr 1899. Foster is a coal miner. "Jenny" is likely a nickname. (1910 Foster jones was also a coal miner for Strangford Sys?)
Ah... and if we look back at the 1910 census, immediately after Foster and Harry's listing is John Stuchell and wife Effie J., and living with them is "cousin" Stella Jones, age 11 (!)
But was "Jenny" the daughter of Delila and David Myers of the 1900 census? We know from the 1900 census that she was born Jun 1875. So she should be a five year old in the 1880 census. We find David and Delila Myers in 1880 in Washington, York Co., PA with 3 children: Cora (8), Jane E (5), and Eda? (1). This last girl could correspond with the Edith E, born 1869, in the 1900 census. And Jane E is the right age to be "Jenny" of the 1900 census.
SO... all this indirect evidence supports that a woman with the name "Jenny" (which might be a nickname of Jane E), dau of Delila (____) and David Myers, born June 1875, married abt 1898, Foster Jones and had at least three children-- Stella (1899), Harry (1902/3) and Hazel (1903/4). That by 1910, she died and her children were spread out among relations.
What this does imply is that Harry's mother was not a Margaret, but a Jane/Jenny. Now recall that Foster Jones had a sister named Margaret, and in 1910, Foster and Harry were living with that sister. She likely contributed to the raising of Harry.
(I looked for Foster and family in 1920 couldn't find him; Harry is 16 and boarding in Burrell, Indiana Co., PA; there's a candidate for Hazel Jones as inmate in an alms house in White, Indiana Co., PA... I don't find Stella; hopefully she's married by 1920.)
This was fun...