[Lord Elrond]

Okay I just finished reading all the postings and I think I can very accurately say many things. First Melian was not a sorceress as we think of sorceresses. She was a Maiar spirit which can be sort of interpreted in modern day description as a lesser god or angel not sorceress. She had special powers no doubt as lesser gods do. If you compare it to Greek mythology it might be easier to comprehend. She could do certain things which mortals or elves could not do but she did not have much power or authority to do stuff outside of her realm e.g. posidon. But she was not an istari, sorceress or wizard
Also there is no way Rhadagast and Tom could be the same people because Gandalf met Tom outside of the Old Forest and it clearly states that Tom's realm is the old Forest and Rhadagast dwells at Rhogosbel.Also Tom rather likes Goldberry and makes constant mention of her Rhadagast does not. There are many more proofs as well.
Finally it only said that Gandalf was the only one out of the five that finished his quest. Originally only three were chosen to go to middle earth to fight the forces of Sauron. Rhadagast was not one of them, neither was one of the Blue wizards, Palando I believe. So these two might have been sent to middle earth under the pretense to help the other three but with little side missions of thier own.