I also wanted to add, in case you are not aware, that judaism does not recognize conversions away from its faith, so it doesn’t matter what church your maternal grandmother/great-grandmother was affiliated with, or if anyone was baptized, confirmed etc.
Anybody born a Jew always remains a Jew according to Jewish law. And anyone born to a Jewish mother is Jewish ( again, even if said mother converted to Christianity, because Jewishness is forever).
Also, you may find it interesting to read about spanish Jews returning to their roots, but realize that they would have had to trace (and prove) their maternal roots back over 500 years to verify their Jewishness and not need to convert, your situation is a piece of cake comparitively.