Dungeon Siege III

This relates to completing Gunderic Manor.

At the end of the dungeon, defeat Lord Gunderic. Exit the room he's in and Leona will be there waiting and will auto initiate dialog. When talking to her she says she wants to take possition of the mansion.

Select the option "Fine... for now" to earn this achievement.

Select the other option if your trying to get

Legion Caretaker
About an hour or so into the game you will meet Leona who will ask you to make sure Gunderic Mansion is safe for her. If you agree, follow the "Quest Breadcrumbs" (up on the d-pad) then fight your way through the mansion saving often.
Once in the Library of Arcana there is a gate with a lever on the wall. The first time you see the gate you cant open it so fight your way through the Library.
After defeating a bunch of priests you should now have the Coalfire Stone so then when you see the gate next, use the Coalfire Stone option. You will now be in the Inner Sanctum.
Save the game now. In the room to the left is the Heartstone to save Alice Gunderic and forwards is the fight with Lord Gunderic, once he is defeated Leona is waiting outside the room. When she speaks choose the options to keep the mansion for the Legion. The achievement now pops.
You could reload the last save, fight Lord Gunderic again then choose to give the mansion to her to get the Lescanzi Ally achievement.