Your examples is ridiculous, because people who would deny the resurrection would not qualify by definition as Christians.
What about Jews who aren’t Kosher? Or Catholics 60yrs ago who ate meat on Fridays & used birth control. Is it your place to say that they aren’t really Jewish or Catholic ? And what about Christians who pick and choose which parts of the Bible they believe ?
I worked with a woman whose husband is a missionary...he believes every word of the Bible is God’s word as written - Old Testament & New. In other words, he doesn’t believe that a story may be an allegory or parable. Are people who don’t, not Christians?
It’s not for me or you to say.
Your Quran quote doesn’t define islam or what is necessary to be muslim. There are millions of muslims who don’t even follow the basic Five Pillars of Islam - they may pray 3 times a day instead of 5 or not fast as they should during the entire month of Ramadan.
It’s not for anyone else to define them as ‘not really muslim’.
Have you actually read the Quran? Yes or no. I have.