The New Enchanted Forest.
The most logical explanation for the events of Season 7 is that when Regina unites the realms, she is only able to unite the realms of the main reality because if the NEF, and WR became part of the United Realms this would cause major past, present, and future issues.
Weaver and WR Rumple died in the finale that is correct. However Weaver's younger self Mr. Gold at that point would be travelling the Realms with Belle which wouldn't be too difficult now that the realms are united. It's 10 years after leaving Storybrooke that Mr. Gold trys to throw away the Dark One's Dagger, and it's another 8 years before he and Belle relocate to the Edge of Realms, and the years they spend living there is only a blink of on an eye in other worlds. After Belle dies he spends the next 8 years in the NEF looking for a way to relinquish his powers without putting a burden on Alice, but time moves faster in the NEF. However at the time of Regina's coronation he would either be preparing to go travelling, or would have already left, but he would still be alive which means if (emphasise if) the series was revived the events of Season 7 could be altered because someone could warn Mr. Gold and Belle of the events that are yet to pass.
Adult Henry and Sir Henry are present at the coronation. Storybrooke Henry did take a graduation trip with Emma and Regina, shortly afterwards is when he journeys to the NEF. However by the time of the coronation he will have already left for the NEF because when Regina, Emma, and Hook come to his aid is when Emma tells him she's pregnant, but at the coronation she and Hook arrive with their newborn child. This is what creates the theory of only being able to unite the realms the main reality.
WR Queen was banished after failing to cast the Dark Curse, Serum Queen relocated to the WR. At the time of Regina's coronation, her younger self would be in the NEF with Adult Henry. Again the 1 reality united theory.
Zelena West is at the coronation because after defeating WR Rumple, Storybrooke Zelena and Robin's younger self relocate to another realm where time moves faster and they return to Storybrooke shortly after Regina went to help Henry in the NEF. Robin is 18 at the time they return to Storybrooke and this is when Robin summons Gothel. After saving Robin from Gothel, her and Zelena relocate to the NEF for 8 years where they join the resistance and by the time Drizella's curse is cast Robin is 26.
Conclusion:
Drizella's curse is all just one big Predestination Paradox and it apparently lasts for 3 years so Hyperion Heights has existed since end of Season 3/start of Season 4 which explains how Storybrooke Henry gets a phone call from Adult Henry at the time of his graduation and this will happen over and over until someone breaks the paradox.
Based on the events of Season 7, 1 month in Storybrooke is 1 year in the NEF. So after Emma informs Henry she's pregnant, Henry has a child of his own, and eight years later Drizella casts her curse, so the 8 - 9 years that pass in the NEF would only be 8 - 9 months in Storybrooke meaning that Drizella's curse would be cast sometime after Regina's coronation.
The only one I'm having trouble with is the 18 years after leaving Storybrooke is when Mr. Gold and Belle relocate to the Edge of Realms. If 18 years had passed while they were travelling then 264 years would've passed in the NEF which makes no sense since Mr. Gold arrives in the NEF shortly after Regina. Only logical explanation I can think of is that he and Belle relocated to the realm that Zelena did where time moves faster so they could both travel and raise Gideon at the same time. However as I mentioned if (emphasise if) the series was revived then the events of Season 7 could be altered because someone could warn Mr. Gold and Belle of the events that are yet to pass.