I think I may have found the answer...
US census 1930, Gloversville, Fulton, NY
Eugene F Provat, head, born NY, age 67
Elizabeth B Provat, wife, born NY, age 67
Eugene C Pronk, nephew, born NY, age 9
That suggests indeed that Eugene Pronk was the nephew of Eugene F Provost/Provat (not of Elizabeth, relation is always to the head of the household).
NY state census 1925, Gloversville Ward 04
Eugene Provost, head, age 62
Lizzie Provost, wife, age 63
Eugene Pronk, grandnephew, age 4
Grandnephew and not nephew, this makes more sense agewise.
A son of the niece or nephew of Eugene Provost.
US census 1920, Fulton, NY
Eugene F Provost, head, born NY, age 56
Lizzie B Provost, wife, born NY, age 56
Luella M Pronk, niece, born NY, age 19, married
Clarence J Pronk, nephew-in-law, born New Hampshire, age 33, married
So it is very likely (almost certain) that Clarence and Luella Pronk are the parents of Eugene Pronk!
They both must have died somewhere between 1920 and 1925.
Now as to Luelle M Pronk:
Her maiden name was Miller.
US census 1910, Gloversville ward 5, Fulton, NY
Eugene Prevost, head, age 47
Elizabeth Prevost, wife, age 47
Luella M Miller, niece, age 10
Using the census records (indexes and sometimes images available on familysearch) you can find your way back to the gg grandparents, etc.