Article Authorship Conflict
Letting aside the messy aspect of the question as highlighted in the comments, let me address your main concern.

Since all three of you agreed from the beginning that you are all going to be first authors (not sure how this works in practice), and you gave your best effort and time in good faith during the preparation of the manuscript, there is no ethical issue in you being first author.

In one of my papers, it has happened to me that the section I was mostly involved in writing turned out to be removed in the final version. Nobody, including me, considered removing my name from the paper.

Now, I don't see why you should be so concerned about how your colleagues acted (apart from the issue of removing "first author status", which I understand is not an issue anymore). They did not like what you've written and they decided to rewrite it. This is good proactivity of their part. If you think something important has been left out, you should try to convince them, with sound arguments, why you think this things are important.

Note that the main concern should be the final quality of the paper, not who wrote what and why. In fact, you should also review what they have written and provide feedback (rewrite what you don't like, and so on).

But bear in mind that in the end, all three of you must agree on the final version. Just know when it is relevant to disagree, and when it is best to let it go.