A character (even a Hobbit) may be brought into play with direct influence at any Free-hold, Border-hold, or Ruins & Lairs.
A character may be brought into play under general or direct influence at any Shadow-hold, Ruins & Lairs, or Border-hold. This does not count against the one character per turn limit.
You may bring these followers into play during separate organization phases.
You may bring this follower into play during your organization phase.
You may bring Aragorn II into play with Strider's company, removing Strider from the game and automatically transferring all cards on Strider to Aragorn II.
If one assumes that some random comment in a player's guide constitutes an ICE Ruling:Each Black Horse in your Ringwraith's company allows you to play one Ringwraith follower who requires no direct influence to control.
The Witch-King's ability is in addition to the one character/turn limit.
Khamul's ability is in addition to the one character/turn limit.
Black Horse allows the play of the RW follower at any time and in addition to the one character/turn limit and at any site.
Strider allows the play of Aragorn II at any time and in addition to the one character/turn limit.
However, this is obviously not what the CoE feels to be the correct interpretation, because they have ruled that the Witch-King, Khamul, and Black Horse must all follow normal character play rules.
Therefore:
Aragorn II can only be brought into play during the organization phase. This is not in addition to the one character/turn limit.
The only effects of Chance Meeting/We Have Come to Kill are nullifying the home site rule (Hobbits in the case of Chance Meeting) and the one character/turn rule (in the case of We Have Come to Kill).
Most of these cards use the exact same wording. Black Horse is a (slight) exception. The aforementioned principles for making the rulings have clearly not applied to half of these cards. Which half, somebody's got to decide.