What if any difference does it make if I wipe out the Witches in the coven. Is there any detrimental effect or should I just kill one for the head. Anyone have ideas? Thanks for the help in advance.

It just means you have to go back to kill them again later on to get heads for the Purity Quests.

Also some guards will comment that you have wiped out or defeated the witches of Glem. if you do wipe them out. I've noticed though doing this and having the witches head in the inventory can sometimes bug the Purity Quest. But I ended up resolving this by droping thier heads and picking them up agian.

So I should probably go ahead and get them all I guess??

Up to you. Those Hagravens are deadly at range for low level players, but pretty weak in melee combat situations.

If you have a head in your inventory then it can make you jump if your just casually flicking through, so be careful.

I one-shotted them with a bow, but this probably doesn't work if you don't have a decent archery skill level and a good bow (and possibly poisons).

it took a few shots with my bow and a stab or two to kill each of them.

i recommend killing all of them at once.

this way all purity quest are available to you without the hassle of going back.