There is an easy way to get all the Legendary creature (killing 10 of one animal). When you explore the area they are in, lead all the animals to a nearby structure (or building).
For the wolves, there is a building on the hill. Now, this is the only one where they will actually come into the building because it is so run down, but there is a walkway/plank near the door. Stand on it, and shoot all the wolves, they can't get you.
The boars' hunting ground has the same with a run down half building (by the shoreline) but they won't attack you in the building.
The cougar grounds probably has the most difficult building. There is a house on the top of the hill. The best way to do this is have a buddy on horse lure them to your direction. When the cougars walk in front of the door/windows, shoot them.
The bears' hunting ground is probably the easiest of the bunch. There is a cabin, that has plenty of open area to shoot the bears from.
And for those who keep asking about unlocking women or legendary characters, those unlock with EXP points. There's no secret task, just build your ranks.