Today, Frontier Airlines and Spirit Airlines revealed that they would be merging to create a single airline entity. According to the airlines, the pairing would mean $1 billion worth of savings for future passengers. The new airline would remain under the Indigo Partners umbrella, where Frontier Airlines sits today.
they are merging but it seems that Frontier is buying spirit for the merger, IDK what you mean by different sources have different opinions. My article that I linked pointed to who bought who for the merger which one airline did need to buy out the other