Here's a guide for Anders, Jorgen and Jostein. You should be able to get all their images with this.
All 3 barn boys require that you pick their team and do a successful ritual with them at the end of CH2, so they're exclusive with each other. They also don't seem to have any relation needs in CH3 since you should end pretty high with them after the blot anyway.
Anders
CH3: story in the barn, woods(look for Anders) and outpost. In the woods say that you stand with progress or the Gods, he doesn't like you being indecisive.
Jorgen
CH2: Must confess that you like him/other boys. Asking him to runka during the 2nd camp night will unlock image 24 after you lock his romance.
CH3: story in the barn, fields and deep fields. Tell him you are not a child anymore during the scene at the fields.
Jostein
CH2: During the 2nd camp scene the choices must be kiss him, apprentice, I like you and you're loyal. Hug him, pick "I would rather tempt you".
CH3: story in the barn and steeds. Make sure to have some sugar or 3/9 huldra skill before you give him his quest items.
Keep in mind that all guys have a side quest and you can't receive a second one from the same group without finishing the active one, so finish any side quests you receive asap.
EDIT: I found one my save files that can work for any of the 3 guys. It's right at the 2nd camp night and all that's left to do in the area is fight the boss. You can also do the fight in the Platform area and use the cake for extra points with Borge.
This save should also work with Tyr(pick "no one must die" at the council meetng) and Erland if you gift him nice clothes.
Pixeldrain