They didn’t. Crestin is aware of Faetal’s existence but Faetal absolutely refused to be anywhere near the Huthian’s or their kind until after Crestin’s demise. He doesn’t trust people and he trusts hunters even less.
Gratia is Crestin’s (Arro’s dad’s) mother. Their name, Huthian, is actually passed down from her side of the family, the man she married wanted to be associated with her name since he wasn’t from a super awesome hunter family so he went “DUDE LET’S KEEP YOUR NAME”. So that’s what they did.
She used to hunt monters, too, but she’s retired. She thinks it’s necessary there are hunters otherwise monsters would eventually RULE THE WORLD or just destroy humanity. She also thinks all monsters, no matter what, are evil and deserve to die. Part of why she’s incredibly uncomfortable with Arro is because he’s so close with Denre, and she thinks her son’s death was a result of his naivety and trust in monsters (it had nothing to do with him trusting monsters).
She’s been teaching Illya how to hunt, but she also teaches her WOMANLY SKILLS like cooking and sewing (but she teaches it in a more survival-way instead of a please-your-husband way). They’re pretty close, Illya really looks up to Gratia but sometimes they disagree on certain things.
Gratia doesn’t look as old as she is because she’s led a very active and healthy life. If you get close enough you can see the wrinkles in her hands and face suggesting age but you wouldn’t know it just by looking at her. She’s a small woman, petite but lean. Her hair’s black and hasn’t started to really grey, yet, there’s a few strands here and there but they’re pretty much unnoticeable. It used to be long but she’s cut it short to make it easier to maintain. She has the same black eyes Arro has and a bit of his attitude, too. THEY’RE BOTH INSANELY STUBBORN AND SARCASTIC. But she’s a little more quiet and reserved and doesn’t curse as much as he does.
Denre actually came to them because he wanted to learn more about the hunters (he wanted at their personal library). He approached them after Faetal said he’d heard Crestin was a whack-job who seemed to like monsters so Denre figured he’d give it a shot. Crestin was ecstatic.