Each character starts with 15 relationship if you play in Normal level, 20 if you play in Easy and 10 if you play in Hard.
There are 10 scenes with each character, and each right answer usually increases by +5. So if you pick all right answers you can get +50 points, which means even at Hard difficulty you are at 60. Some characters have little more scenes, others less points, to have more harder characters to get. Also, you can get points for a characters also participating in a different romance path. For example one of the scene of Morgan's path can bring +5 to Sebastian, to John, to Jonathan and so on.
I will list only the right choices of each character path, leaving the other one for you to discover
Remember that at regular intervals there are also miniscenes where you can join someone at the tavern and that will give you +1/2 points, or some characters might invite Heileen (this happens towards the end of the game) and if you accept you can get an even bigger boost.
Morgan and John are the easiest characters to romance. Jonathan is mid way and Sebastian surely is the hardest one.