This quest bug is awful! But following your method worked for me, it just took a while because of respawn times.
First I re-bound my interaction key so that I wouldn't accidentally press it via reflex (so tempting to loot the golden-glow bodies...). Then I found a single, lone "Heritance" enemy so that I wouldn't get murdered from a group of 2 or more and so that I wouldn't get confused about which bodies were which. I led the original enemy away from its spawn a bit and killed it and left that body alone, then I returned to the spawn. I'm not sure if this part is necessary or not, but I did it just in case.
I waited for respawn and killed that enemy on its spawn point, but still didn't plant any seeds; I refer to this body as a "good" corpse. Then I waited for the next respawn, waited for it to start to attack me, then planted the seed as it stood on the "good" corpse, which planted the seed on the living one. After that I led the now-skeleton away from the spawn a bit before killing it to ensure that I wouldn't confuse its skeleton body with the "good" corpse. I then returned to the "good" corpse at the spawn, waited for the next spawn, and let it attack me and planted another seed on the living one as it stood on the "good" corpse, then led it away before killing it. After that the "good" body vanished, so I killed the respawn where it stood but didn't plant any seeds on the body, allowing it to become the new "good" corpse. I repeated this until reaching 6/6 seeds planted.
The single enemy I found was up the Eastmost ramp, and behind the Northmost house. There is another single enemy just on the west side of the house, but it walks around; the one behind the house stands still. There is enough space between it and the nearest enemies that you should be able to fight it without worrying about alerting other enemies. Also, very few people went all the way back there, so there is less of a chance of issues happening from another person messing with the enemy.
You guys posting without reading?Probably wrong corpse? Has to be a human and it takes several attempts with E while getting beat on. I didn't wait for a respawn, I dragged another NPC over to the corpse. Note in the screen minimap where I was at, nice spot. 1 npc that walks around a little. He walks over to where 2 Heritance NPC's spawn. Plus 2 more NPC's across the little pond, within ranged attack distance. So total of 5 NPC's there.
Ended up with a pile of corpses and I was able to loot them all LOL