That there were two wives is a possibility, also (note that it would likely have been the reverse: Chaya Rost would have been the first wife; her daughter Sossie was older than the other known children). Though that interpretation is not without its potential problems, either, given the limited information in the original post:

• The listed age of the Sossie who died in 1884 (daughter of "Chaya Rost") does not quite perfectly match the birthdate of the Sossie who was born in 1875 (daughter of "Gittel")
• It would require us to assume that the OP's knowledge of her great-grandfather's birthdate is off by ~5 years - he would likely be the Chaim Elia born to Gittel Kurz in 1877.
• The OP stated that she believes that her gg-grandmother's name was Chaya Rost - I assumed this came from family lore or from some US vital record rather than from searching JRI-Poland. But the mother of the Chaim-Elia who was born in Czortkow in 1877 is specifically listed in the index as Gittel Kurz.

I am tempted to think that "Chaya Rost" could actually be the same person as Gittel Kurz, that she had a compound name like Chaya-Gittel, and that the "Rost" could have come from the tendency in Galician records to use a person's mother's maiden name as their surname when their parents did not officially register their marriage. The problem with that is that if her name was really Chaya-Gittel, it seems unlikely to me that she would have namedone of her own twins "Chaya" in 1877. There is also the problem that a search in the database shows loads of other people named "Rost" specifically in Czortkow, suggesting that that might have indeed been Sossie's mother's surname rather than a translation/indexing error resulting from the bad condition of the original pages. None of these other Rosts are from Jezierzany.

There is a likely match for one of Gittel Kurz's daughters, with the English name "Jennie," marrying a Morris Weissbrod in Manhattan in 1903:
https://www.familysearch.org/ark:/61903/1:1:24H3-ZL4
https://a860-historicalvitalrecords.nyc.gov/view/8399994 (caution: this link may not be permanent)

There is a Jennie Weisbrod who died in the Bronx in 1961 and is buried in Mount Hebron Cemetery - and the stone lists her name as Zlata bat r'Yitzchak Yosef - suggesting that she was highly likely to have been the Zlata Kern listed in the database as a daughter of Isaac Josef (Alter) Kern and Gittel Kurz of Czortkow, born in 1880.

If the OP knows that Jennie Weisbrod was a sister of her great-grandfather, maybe that is sufficient corroboration that at least the "two" Alters listed in the records are actually the same person?

Curiously, one of the witnesses listed on this marriage record was named Max Rost.

Adam Turner