Do I still have any rights if the DNA tests came negative?

There are a lot of factors that go into what your status is regarding these children, however even an unrelated 3rd party (which is what you technically are) can still state a claim for custody if he or she has (1) created a substantial relationship with the minor children and (2) the biological parents have acted inconsistent with their protected status as parents. From the limited description you gave, it sounds like you have a substantial relationship with the children. As for part 2, you can make an argument that Mom's allowing you to act as father to the children and exercise decision making over their health, education and welfare is an act inconsistent with her protected status as a parent. You will need an attorney. Third party custody is a complicated area of the law.