Which group of organisms evolved from the same ancestors as amphibians?

It depends on which ancestors of amphibians you're talking about. If you go back to the first life form, then all organisms evolved from the same ancestors as amphibians. If you just go back to the most recent ancestors common to amphibians and some other class, then reptiles, mammals and birds also evolved from that ancestor. Reptiles, mammals, birds and amphibians together comprise the tetrapods.