A pair of gloves can be found a bit further down the road belonging to the killer of Gareth's family, upon giving him the gloves of the killer, he will request you to find and kill Jonathan (The Killer) and he can be found in the black pits with an elf strung up, who is connected to another quest

you will have to convince him revenge is not the way and the quest will be closed with him on the ship

My dialogue is the same i can do anything to make him stop digging. I killed jonathan have the ring AND the gloves but still, i cant do nothing.

If you have the hero tag and you have a wits check where the quest will complete right away he'll stop digging and giving the party 8075 exp

I helped him get revenge but he vanished from the farm after so I can't make him come back to the ship.

Many ppl talk about a bug If you help Gareth in his revenge against Jonathan, for the death of his parents . Eventually Malady tell you that you must find Gareth before leaving reaper's coast to the Nameless island and you can't find him anywhere. It's not a Bug at all it's the story: you convince Gareth pursuing revenge, so you will find him later in the nameless island, the next act, since he leave before you for his revenge against the order.

Tips & Tricks: fix the part with the parents. You can Interact with them, at least eventually, they will ask you to clear the house of the voidwoken, will reward with a pouch with items that belonged to Hannag. Probably unlocks new dialog for Hannag when you first meet her.

You can interact with Gareth's parent by killing Jonathan in the burning house near Driftwood Filed and select You understand Gareth's felling, where you might need to convince him later on since he's so upset about your action(I didn't up to that part yet). When you arrive at Gareth's home, you will find his parent is hiding behind a cart outside of the house, and you can talk to them and agree to help them clear up the voidwokens. Killed all voidwokens in the house, and report to them, you will receive a pouch that belonged to Hannag, and they will return to their house. You can talk to them inside the house for few dialogs. (better to clean up the surface since they don't have any magic armor to resist the poison or whatever left on the ground)
The pouch included few items(a scroll and a grenade in my case, I guess they're randomly generated) and a unique ring of Hannag, which worth 1500 gold without any special stat. Not sure if there are any new dialogs since I already met Hannag and no new options unlocked at this moment. Killing Jonathan will unlock the Steam achievement for set Gareth on a path of vengeance immediately

For me, I didn’t have Spirit Vision, but high persuasion. I killed Jonathan and took his ring. But, weirdly he still had his items(gloves) scattered about on the way to Blackpit. I told Gareth to cool it and go back to the ship. I met his parents I couldn’t interact with them until I completed the blackout quests. They then told me to clear out voidwoken. But, now the guest is still open like Jonathan is still alive?