The individual shots too.

The separation of the human and worgen forms should have been in the game from the jump. That being said my headcanon for him having white hair/fur now is due to the shattering of The Helm of Damnation which in my option would have some effect on the Death Knights. Also Blizzard Worgen could still use some jewelry options. 

For Callahan and Garmm their respective groups of Paladins and Death Knights go to investigate the stuff that is happening in Drustvar. For me, there is still tension between the two groups after the stuff that happened during Legion with Tirion. During one of the attacks on one of the towns in Drustvar Callahan and Garmm run into each other and with the Order of Embers not trusting none of the DKs Callahan speaks up for Garmm. The two decide to put their differences aside to aid the people of Drustvar.

During their time there the two meet the Thornspeaker druids and one of them being Garmm and Dylan's uncle Dorion. Garmm had no idea about him as it was a kept secret because Garmm's grandparents didn't approve of Dorion's calling of becoming a Thornspeaker druid.

The reason why Dylan is there at the time because he is part of the group who is trying help find Jaina and arrives to talk to Ulfar. Dylan's mindset is just to get his job done and go back to help the 7th Legion against the Horde for what they did at Teldrassil. So he pays little attention to his so-called uncle who really wants to talk to him.

Name: Garmm Grimmkell

Age: 42(BFA) 35(when raised as a Death Knight)

Height: 6'2"(Human form) 7'(Worgen form)

Weight: 180lbs(Human) 268lbs(Worgen)

Race: Afflicted Gilnean/Worgen

Gender: Male

Nationality: Gilneas City

APPEARANCE

Hair: Grey-black, short, mustache, goatee, and beard.

Skin: Dark skin, but pale from being dead

Eye: Glowing Blue

Build: Muscular

Uniqueness features: has a ring around the bottom part of his beard both in human and Worgen form. And another ring around his right bottom canine while in Worgen form. His bottom canines are also a bit thicker than his top ones.

Personal Stuff.

Class: Warrior (when alive.) Death Knight

Profession: Knight of the Ebon Blade and one of the Wolves of Northrend.

Hobbies: Took up skinning(a suggestion from his brother to help with his need to cause pain) Hunts a lot. Protecting his brother Dylan.

Languages: Common and a few other languages(had to communicate with fellow Death Knights for missions).

Home: Ebon Hold and Drustvar(after clearing out the witches.)

Birth Place: Gilneas City

Relationships.

Mother: Nita Adkins-Grimmkell(died in 2nd War)

Father: Dwight Grimmkell(died in 2nd War)

Uncle: Dorion Adkins( didn't know about him until meeting him in Drustvar)

Younger brother by 15 years: Dylan Grimmkell.

Additional information:

Garmm started taking full care of his brother a few months after he was born as their parents were killed during the second war. He made three oaths that day; one to his parents to always care and love his brother, one to the Light to always protect him from any who would harm him and to Dylan himself to always keep his promises. Both of them share a very strong brotherly bond that allows them to almost sense each other even when they are far apart.

He was one of the many warriors who went to defend the Greymane Wall when the scourge made it's way to Gilneas and when Arugal summoned the Worgen to "help" take care of the scourge. Instead of returning like he promised his little brother he and others tried to lead the Worgen away from the Greymane Wall when they started attacking them. He was bitten then soon after transformed into a Worgen. He was one of many who were taken in by Arugal who had him and others under mind control. During that time as he slept when he could, he was able to see small visions of Dylan growing up without him. This would allow him to get some semblance of control back and he with some other Worgen escaped. However, sometime after they would run into some of the scourge lead by San'layn and were captured, killed then taken to Ice Crown to be raised as Death Knights under The Lich King.

As a Death Knight bound to the Lich King's will Garmm like many others would commit a lot of atrocities. One in which Garmm kills a Paladin who was the mentor to a younger Paladin named Callahan. Both he and the young Paladin would meet again at Lights Hope and Garmm would regain his own will back. He would help during the campaign against the Lich King and would stay behind to clean up the rest of the leftovers from the former Lich Kings' reign.

When he found out what happened to Gilneas he almost went into a berserk frenzy against the former Horde Death Knights. He and a few other Death Knights the Gilneas Kingdom went back to check out the city only to find it in ruins like the reports said. Gramm's brotherly bond with Dylan would yet again manifest itself again during the battle of Ashenvale and sensing that Dylan was about to be killed Garmm can Death Gate to his little brother’s location to save him and feed his need to cause pain to others. He shows up in time to save Dylan and cut down a lot of Horde forces.

Garmm didn’t know the Worgen he saved was Dylan until Samantha a priest from Gilneas(was saved from being turned Worgen because of Dylan)  and childhood friend to both bothers called his name and he got a good look at him. Thus the brothers Grimmkell were reunited. While Dylan was happy to see his brother to the point of crying when he hugged him Garmm with his emotions dulled didn't know how to feel.

“Tirion!” 

 Callahan wasn’t sure who called out the name as the sight before the Paladin filled him dread. Looking around he could see that everyone had stopped to see the strongest of all Paladins at the mercy of that monster Gul’dan.

‘The Light will protect him,’ Callahan thought to himself. 

The battle against the Legion had been endless and all he remembered was fighting, fighting and more fighting. Looking around to his right he caught sight of Garmm Grimmkell the Worgen Death Knight who like him had been part of the first wave of forces on The Broken Shore his glowing blue eyes seemed to glow with a darker tone when seeing the orc warlock. Next to him, a little ways off was his younger brother Dylan, the Worgen rogue his daggers known as The Fangs of the Father,  Golad, Twilight of Aspects and Tiriosh, Nightmare of Ages at the ready the eyes of both of them looking every which way. 

‘The Light will protect him,’ Callahan repeated.

To his left, the Paladin could see Samantha the Gilnean priest who was not cursed like Dylan and Garmm had a look of horror on her face clinging to her staff like it was a lifeline. Next to her was Chow Prowlpaw the Pandaren monk his robe long gone but unlike most of his race Chow was stacked with so much muscle one could see their definition through his fur the only thing that seemed out of place was his gut. His jade and emerald eyes set with resolve.

‘The Light will protect him,’ the Paladin thought again.

Chow, Dylan, and Samantha arrived with the forces led by Genn Greymane and Lady Jaina Proudmoore while He and Garmm arrived with the Paladins, Death Knights and the first wave of Azeroth’s forces. However now all those forces were all staring at the sight before them.