Blossom wrote:I am confused about what Mahayana Buddhists believe about the six realms.
Are they representations of the fluctuating life states of humans, or are they actual realms which people are born into?
A nun told me that she prayed for hungry ghosts, which she said we cannot see.
However, the SGI teaches that hell beings and hungry ghosts are not otherworldly, but material people.

I think that describing the six realms have some purpose. It is taught in order to teach us about the results of ignorance, superior feelings, inferiority feelings, hunger, greed, anger and such. Like god realms is a medium to teach about greed. Let's say human beings with too much wealth, live a wonderful life, yet they act as they are like god and are way too greedy. That results in rebirthing in one of the six realms and according to the cycle of samsara they will be reborn in the lower realms and cannot escape this cycle of rebirth until and unless they achieved liberation.
You also talked about Hungry ghosts. What are the hungry ghosts?
they might be supernatural beings than human beings. But imo, hungry ghosts are the medium to teach us the unsatisfying hunger, craving for new things in order to satisfy our hunger, this hunger keeps on rising.
same goes for other realms.
"Thousands of candles can be lighted from a single candle, and the life of the candle will not be shortened. Happiness never decreases by being shared." Lord Buddha