This is another story related achievement from the Fable: The Lost Chapters content. There will be spoilers, so if you are happy knowing you will get the achievement regardless of what you do, so long as you keep progressing you can feel at ease. If you're curious as to what lies ahead, read on...
*** Spoiler - click to reveal ***You have options on these quest objectives.
The first soul you must collect for this quest can be either Thunder's or gathered from the Arena.
Option 1: My choice was to spare Thunder. When you enter the Arena, you will have to face waves of enemies before you can collect the soul. 2 waves of Minions and Trolls, 2 waves of Minions and Balverines, and 2 waves of Minions and Summoners.
Option 2: Kill Thunder. I didn't go this route, but looked it up see what you'd go through. My understanding is this is basically the same as when you fought him (if you fought him) to marry Lady Grey.
Next, you must either retrieve your mother's soul from Oakvale Memorial Gardens or kill Briar Rose.
Option 1: Here, I went for the mother's soul. When you enter the cemetery there are numerous Screamers. One will be inside a ring of fire. This one should be your primary target. When it dies, you are done here and can collect the soul.
Option 2: Kill Briar Rose. I read up on this one too. It seems Briar Rose uses the Drain Life spell, the Heal Life spell, and an Illusion spell (to make you see multiple of her). Just wait for the illusion to fade and attack the real her.
The last soul you must collect can be either that of the Guildmaster or Nostro's Soul from the Circle of the Dead.
Option 1: I decided to go for Nostro's Soul. Fast travel to Lychfield Graveyard. You will have to fight your way through the Old Graveyard Path. When you reach the Circle of the Dead, you have to fight Nostro for his soul. In order to harm him, you must first kill 1 of his undead underlings. When they die, he can be hurt temporarily. When he turns transparent again, kill another underling. Follow this pattern and his soul will be yours.
Option 2: Kill the Guildmaster. I looked this one up too. Head to the Guild Woods. Here you will be fighting the Guildmaster's guards. He will cast Physical Shield on them and heal them. Once they are defeated, his soul is yours.
When you return to Archon's Shrine the last time the quest will be completed and you will get your shiny new cheevo.
*** I've had an idea. Because this game lets you play any way you want, everyone is going to develop a fighting style they are comfortable with. Since everyone is going to have their own way to handle these fights, I'd like to encourage the TA community to post their strategies for the actual fights in the comments. Anyone looking for actual fight techniques can go there and find out what works and pick the style that works best for them (this was why I was reluctant to do a blow-by-blow of how to handle the fights...and because Fable isn't really that difficult with regards to the combat
)***
Thanks to DJH4311, the first commenter, for taking the initiative to post his thoughts on the fights. This inspired my idea.