I'm not too familiar with Elves, but I do have some experience with interviewing dead people. In my area of expertise, it's generally considered to be bad historical practice. Even if you manage to interview one who has all his vocal tools intact, their ramblings are generally incoherent. Any form of context derived from such interviews is mostly imposed by the interviewer and it rarely leads to solid information, let alone information you could use while writing a thesis.

That being said, I have no experience with coherent dead - like ghosts or spirits. I can only assume that the same scrutiny applies to such an interaction. Keep in mind that the dead are rarely concerned with our problems. They have little notion of the things we would consider to be noteworthy. It would be ahistorical to assume that their worldview closely mirrors ours. I guess you will have to wait for an actual expert for a more relatable answer, but I would be very hesitant in using sources like this when writing a thesis. Perhaps you could confer with your professor or promotor first?

Good luck, it sounds like a promising thesis!

While my focus of study if the Dwavrish race (specifically the importance of the Halls for Durin in the Second and Third Age), I can speak with some confidence of the communication from Valinor.

After the destruction of Númenor is was raised into the sky. Due to the translations, we can agree that this was a true event and not an allegory. Therefore, due to its unusual location common methods of communication used by Men are not usable. However, there are ways the Valar had that would be able to bridge the gap with the Elves.

Unforturanlly the number of Elves dropped drastically after the War of the Ring. Many sailed to Valinor during that period and the remaining, if they still have contact, do not share that knowledge [Tel' Alta Lema Meetima Quessir]. It is important to note that Valinor is small and therefore its location must have been communicated between the different exodus groups. How that was done is not known.

I can't answer on Elves but it is widely regarded as fact that the Oral History has to be taken with more than one grain of Melange since millennia of propaganda and religious worship (especially Fremen and Fish Speaker, whose Jihads were also very effective at spreading their interpretations) has made it heavily political.

If we want to go with more reliable sources we have to dig pretty deep in what archives remain after the chaos and war that came with the return of the Scattering. If you're really lucky you can still find scraps of texts written by a person who I'd argue to be the greatest historian of all times, the Princess Irulan (officially wife of Paul Atreides but never consummated).

The only real alternatives would be to go underground and try to track down one of the few remaining Rabbis, since Jewish Oral History is generally regarded as the purest available sources on the past. Of course there are also the Bene Gesserit, whose access to the Other Memories would make them perfect historians if it weren't for their treacherous greater interests making everything they actually are willing to share with you questionable by default.