The wording confused me slightly on the requirement for brutal finish. Can you use this feat with either a two handed weapon or two single handed weapons or just a two handed weapon? Earlier in the fighter section several feats required a two handed weapon while this asks for 'a melee weapon in two hands'. Thanks!
You can use Brutal Finish with any melee weapon which you are currently wielding with 2 hands.
So practically anything you can reasonably grip with both hands.
Relevant Rule:
Some weapons require one hand to wield, and others require two. A few items, such as a longbow, list 1+ for its Hands entry. You can hold a weapon with a 1+ entry in one hand, but the process of shooting it requires using a second to retrieve, nock, and loose an arrow. This means you can do things with your free hand while holding the bow without changing your grip, but the other hand must be free when you shoot. To properly wield a 1+ weapon, you must hold it in one hand and also have a hand free.
Weapons requiring two hands typically deal more damage. Some one-handed weapons have the two-hand trait, causing them to deal a different size of weapon damage die when used in two hands. In addition, some abilities require you to wield a weapon in two hands. You meet this requirement while holding the weapon in two hands, even if it doesn’t require two hands or have the two-hand trait.
If an ability requires a 2-hand weapon, then it has to actually be a weapon that lists 2 as its number of hands to be wielded in. A 1-hand weapon with the 2-hand trait doesn't qualify.
If an ability requires a weapon wielded in two hands, then any weapon qualifies so long as you are actually holding the one weapon in two hands. You are allowed to wield a weapon in more hands than required, but unless there is something like the 2-hand trait or abilities such as Brutal Finish, there is little reason to do so.