Is it obligatory to repeat the ghusl if one definitively intended to perform it again but then interrupted it, and is it permissible to change the accredited fatwa authority in search of an easier opinion to relieve obsessive thoughts, and is it permissible to rely on two different fatwa authorities for different matters?

What you did by not repeating the ghusl (ritual bath) was correct, as was ignoring the waswas (whispers/obsessive thoughts) and paying no attention to them. Leaving the ghusl incomplete was correct. There is no harm in acting upon the fatwa of a scholar whom you trust, whether it is our fatwa or that of another trustworthy source. There is no blame upon you, as long as you are afflicted with waswas, in adopting the easiest of scholarly opinions until these obsessive thoughts dissipate from you.