From what I know Now and Then endings with Julie and Hana as main romantic partners were added in directors cut and because of it there are determined mostly by one choice at specific moment beside overall good relations with them to have it. I know for sure that, if in the night after the main attack on Hana's house you chose "Stay in bed with Carol", then the ending will concentrate on a partner with the higher "Love points" excluding Hana or Julie.
Personally I really like, that ending with Julie was added, if you choose "Get up and check the staff quarters", because thought she was less shown than the others, she is my favourite. If you don't choose to visit main house or staff quarters after the battle, then probably the easiest is to get Carol's ending, because she has more opportunities to build close relation / get "Love points", but you can have with others, if you always prioritized spending time with them over Carol, or if many times you made wrong decisions in that relationship. Story of MC and Carol is the core of the plot, plus probably only with her it is unavoidable to start intimacy, so she being at the centre at the end is suitable and main plan of the creators. Yet, I appreciate that all relations have some depth and all potential partners have personality, also that even if you have chosen polyamorous path - the ending isn't the same, but defers depending on your choices.