In general though, if you save often, and before each choice, you can see how much relationship you get. With Ren'Py you can rollback, so if the choice doesn't give you much relationship you can either reload a save or rollback to the choice and pick another one. Using this system shouldn't be hard to reach max relationship with all the love interests!
Remember: If you bring a character with you during a full moon event you get a small boost of relationship too.
(only the first two matters, since the third happens at the end so it's too late for the romance)
For each character I'm listing only his/her "camp talk" scenes. There are more choices during the initial recruitment phase but I believe by picking the choices below it should be already enough to reach 100% relationship (I might be wrong though so feel free to correct me).