When it comes to marriage, they can't officially get married but they can do a symbolic one, and have F marry someone else like Georgina. If you are referring to Lucas as the unpleasant acquaintance, he is still in jail at this point.
As for the new girls, Leah is absolutely the photographer from Melody.
I have a theory on Emily, though I may be wrong:
So far the timeline is the Superstar Ending from Melody is canon in both DMD and Sunshine Love. The walkthrough for Melody says you can't have the Sophia/Xianne lesbian path active to get the Superstar Ending but that is wrong, you definitely can. Melody is at their wedding and people know who she is. They could have Ivy and Lily be the ones organizing Koko's party, and they take Kristina along and that is where she meets D.
Also, yeah, it would be nice to see an Elena and Farmboy scene.