I already did that.
just look at my quests and tell me which one you dont have and I can help you with it1 year ago (+1)
for Elith after completing the Selena quests you will get askes by Bert to go to the sewers and when you eventually meet Elith just lose to her and your relationship will improve, also if you beat the squid after a while you will get the lust fruit and if you beat Elith you will get the ability to summon the squid pretty much anywhere but I don't think it does anything for the current version. 2. for lily once you get through the dwarfen kingdom and make it to the snowy mountains and the hotsprings within you will need help from lily (The fairy) and by battling monsters that improves your relationship. 3. for Vivi once your in the snowy mountains go fight the same boss for another magic fire ball thing and use it on the cave, inside you will find glace and after some time she will take your body to a house where Vivi lives, glace will improve your relationship with Vivi on her own.
EDIT: sorry didn’t see you asking how to complete the selena events. After you get faylen to max level you need to go to the creepy prison shack and use her ability to reveal the evil squid there. After beating him he drops a pendant wear it and go to sleep to see selena if its working before you leave you should talk about nel with selena and that forwards the quests. If it doesn’t work pass a few days and I think it will work