I don't know how to level up Helga and Feran so I kind of cheated.
I beat up countless monsters until their health are low enough to the point where even a child can kill them in one punch.
I used this tactic over and over again and just send them all to Helga and Feran.
Feran bowed his head then stood straight up. "Uwaa... I'm sorry my lord you had to do this. We don't have any fighting capabilities. But I'm sure that our enchantments and healing will be of use to you my lord. Hahaha! Isn't that right my beloved sister?"
Helga had a disgusted look on his brother but Feran simpl didn't mind it and smiled even more. "Tsk." She then looked at me. "Ah yes. I'll do my best!"
"I'm sure you will." I reassured them both. "Anyway this is a great skill Feran. It's extremely useful. I wish I found you sooner."