Can someone tell me what happens to Logan if I choose Bernarde and vice versa?
Well what happens if pretty much the same for both if you choose the other, you help one and the other can be found at the Wolves Den in Werewolf form at night, you can help them and cure them at your home if you capture them.
What it means though and for a more Meta Suggestion (if you want the info):
if you do not Choose Logan you do not gain his first heart and I think you are locked out of his future relationship events and quests (might be different now because Updates but I think very very unlikely) and you will gain 10 like for Bernarde. Though if you choose Logan you can continue Bernards relationship and events.
To keep it simple I would suggest choosing Logan as you can just continue boths relationship events if you choose him so you make win win here.