Most/all stars are getting their energy from fusion of small atoms like our sun. But is it possible according to the laws of physics that there are stars getting their energy from fission fe with uranium atoms?
Well yes, maybe, but they are called planets. So fission in stars? No, but maybe in planets.
I do not know what the status of this is, but the core of the Earth is heated by weak and maybe strong nuclear processes. The standard model is that weak nuclear decay. The major heat-producing isotopes within Earth are potassium-40, uranium-238, uranium-235, and thorium-232. There is a challenge to this which says the core of the Earth also has nuclear fission occurring. This article in Nature discusses this possibility. I have no bone in this scientific controversy. However, the remnants of a natural nuclear reactor in Gabon has been found. So this is not impossible.
No. Basically because stars, by definition, are fusion reactions. It's feasible for a star to contain Uranium - the Earth, for example, contains Uranium, and could (in fairly extreme circumstances) collect enough matter to become a gas giant, continue to collect matter and then start fusing to become a star. But even then, you'd just have a star containing an unusual amount of Uranium, not one that is running on fission.