That's YOUR belief. Not a fact. God is not divided.
Either Saturday, Sunday or Friday is the Sabbath. It isn't whatever you want. God has ONE set of laws for His people, only one faith can be true.
You're a shallow thinker. You need to think this stuff thru
Just because one does not follow the proper guidance does not mean they are not believing in the same G-d it just means they are following the wrong human purveyors of that information.
If G-d tells me when my time here is over "you were supposed to rest on Sunday" while I was say, keeping Shabbat on Saturdays, does not mean I did not believe in his existence or pray to him.
Let us say for argument sake Prophet Muhammed was the true prophet who had the correct message from G-d. If a Jew prays to "Hashem" at night, does this mean he is praying to air?
No, he is still praying to G-d, the one and only. Now one can follow whatever belief one has about their punishment, but it will not be due to them not believing in G-d.
You know in Judaism the belief is that even if one never read the Torah, never knew of mitzvot, the person could be anywhere in the world but as long as they were a righteous person, a mensch per se; they will have fulfilled their obligation to G-d. Righteousness and ethical living are highly valued and can be rewarded regardless if one is Jewish or not.
The problem today is that the loudest voices on all sides of the religious doctrine are trying to solidify their beliefs through strict doctrine while most of the time they are misguided or outright wrong.
Refer to the Talmud: "The righteous of all nations have a share in the World to Come."
Thus, righteous conduct and ethical behavior are recognized and rewarded by God, even if a person is not traditionally Jewish. It emphasizes the value of morality across all nations.
Read up on Tzedakah and Tsaddiq