My guess (and it’s really only that!) is that it works like this?
1) Young Henry leaves SB at the age of 18 in the year 2018, lets say in September to match the S7 premiere date.
2) A lot of time time passes normally. Henry is now in his mid thirties when he meets Cinderella in the EF 2.0. When we see Regina, OG Hook, and Emma come to his rescue in 702, it is now Octoberish 2025-2027. Emma is having an extremely late-in-life pregnancy. This also explains why Robyn is so much older when Gothel transports her to the EF 2.0
3) Emma and OG Hook return to SB 2025-2027; this Emma and Hook are not the same ones we saw in the series finale. They are off living in the last 2020s unaware of everything that is happening.
4) The Curse is cast and it sends everyone in the EF 2.0 to HH and back in time, to pre-September 2018. It’s a random guess but let’s say six months prior, so March 2018.
5) Old Henry calls Young Henry on his graduation, which would roughly be May 2018.
6) Alice and Robyn travel via bean to SB in May of 2018. 2018Regina and 2018Emma are with recently graduated Henry on a road trip. Emma is not yet pregnant (and wont be for another 20 yrs). Baby Neal would now be about 5ish and Robyin 4ish.
7) Regina unites all the realms by bringing them to SB in May of 2018. Emma and Hook become parents much earlier than 2028 Emma did (no one has aged much from the time of unification to the time of coronation)
A big rub here is what happens when 2018!Regina and 2018!Emma come home to 2018!SB to discover that there’s a 2028!Regina, thirty year old Henry, young Wish Henry…..Are there now 2 Reginas in SB?