If you have 0 Relationship EXP with them, you will get 0 Hearts and the "bad" ending.
If you have 225 Relationship EXP or less with them, you will get 1 Heart and the "okay" ending.
Using the cheat code donottrytrainjumpingathome can also be used to unlock Emmett.
In the present, use your computer in The Emerald Apartment and click on the My Documents icon.
The key pattern goes like this if each key is numbered from left to right: 8, 11, 10, 5, 9, 6, 8, 4, 3, 11.
If you have 450 or more Relationship EXP with them you will get their "best" ending.
The second image can be enlarged when selected to reveal sheet music.
Play this song on the piano in The Hayes Mansion while in the past.
(If you are using cheats the cut scene may not trigger, be sure to leave and re-enter the area every so often).
To have a successful date you will need to raise the Mood to 5/5 and kiss the character.
Raising your Relationship can be done by talking to them, giving them gifts and going on dates.