These are primarily going to be Jaywon, as I don't majorly read Heejake, personally. (They're cute and all, just not my OTP.)
Some self-recs, if you're interested:
S O U L L E S S series || In a world where those who retain their cat ears and tails are held up as "innocent" and "pure", Park Jongseong and Yang Jungwon have become used to what that means in the 5+ years since their debut as members of ENHYPEN. But everything about their relationship changes when they receive their shared "true" name... and are thrown together as a spell-battle team. Jungwon is the Sacrifice; Jay is the Fighter. [aka Jaywon Loveless Fighter/Sacrifice AU]
The Last Dance || Park Jongseong is finally getting married… to Lee Heeseung. Jungwon is Not at All Pleased about this news and decides to a) make his displeasure known in spectacular fashion by crashing the wedding; and b) break his cover, finally exposing his true nature as a jeoseung saja to his eldest members. The last dance belongs to him alone, and Jungwon will make sure that Jongseong knows it. [Inspired by Elisabeth das Musical. Slightly AU.]
Eyes Translucent Gold series || Yang Jungwon's world is turned upside down when, on Jay's 24th birthday, he discovers a secret that his hyung has worked for years to keep hidden. More than that, he learns about a whole other wild side of himself that he never knew existed. After returning to Seoul, Jungwon now has to balance his life as a K-pop idol and ENHYPEN's leader with his new reality as a wereleopard, one on the verge of his first transformation... and Jay's mate. [mostly rated Explicit. aka wereleopard!Jaywon AU]
Wild Madness Getting Stronger, Stronger || After a fansign, Jungwon is finally driven to the breaking point by his omega's jealousy (and his own possessive nature). He will claim Jay as his alpha, the resulting consequences and scandal be damned. [Omegaverse. Explicit. Currently a one-shot but planning on turning it into a multi-chapter fic when my current WIPs are finished. Probably going to have Heejake as a sideship.]
Other AO3 Jaywon fic recs:
Fatal Trouble by jaywonism || ENHYPEN as summer camp counselors gone horribly wrong. Very much a horror fic. Rated E for typical slasher themes and eventual fun times between Jungwon and Jay.
Pain Management by jaywonah || Doctor/Patient AU featuring Jay as a physical therapist and Jungwon as his professional dancer patient. (Jungwon is also technically in a relationship with Sunghoon for most of the fic, but it's not a healthy one.)
The Blackmail Game by whis4angels || Mafia AU, with Jay as a mafia boss and Jungwon as his college student blackmailer. [Rated M]
AO3 author whis4angels primarily writes for Jaywon and Heejake, FYI, so if you like their linked fic, you might want to check out more of their stuff.