I searched but found nothing on this.
I know you can only gain one action no matter how many characters with leadership you have, but can I still "succeed" more than once?

specifically, can I have two WOS Wolverines adjacent to each other and succeed both leadership rolls potentially removing a token from each?

here's all the info for reference.

Reluctant but Brutal Leader: Wolverine can use
Leadership. If Wolverine succeeds in his Leadership roll, you
may also remove an action token from an adjacent friendly
character with the X-Force keyword, then deal that character
1 unavoidable damage.

Leadership
Once at the beginning of your turn, as a free action roll a d6.
On a result of 4–6, add one action to your action total for
that turn. A player can gain only one action each turn with
this power, even if the player has more than one character
with Leadership.

Yeah, you can roll Leadership multiple times, though you still only get one extra action.

In your case, though, Wolverine's trait wouldn't allow him to heal back until the next turn since you've taken a non-free action with Leadership.

Actually, this is incorrect. Leadership is a free action taken at the beginning of the turn. As long as you don't make a non-free action after the Leadership roll Wolverine would still be able heal because it is still the beginning of the turn. It's not unlike using Outwit on a damage reducer before using Poison.

Yes you can suceed any number of times but you only gain one action. Other effects still happen

Another question regarding some specific Leadership SP, like the one Namor uses.
Attuma use the same, with just a different name.
If I play both Attuma, Namor and Aquaman (standard Leadership) in a very big Atlantis theme team, if I choose to use Namor's SP to get the second option (2 actions), can I still gain an action by using another Leadership the normal way ?
My first though would be to allow both Namor and Attuma to gain 2 actions using their SP and to let AQuaman gain another one using Leadership, since technically neither Namor nor Attuma have used Leadership the normal way (I know that SP allowing to do something different than gaining actions with Leadership, like the Chief's one, are working like that) but they do gain actions when using their SP so I want to make sure I'm not wrong about this.

So let's say I have a team with all 4 of these guys on it. Because I'm lazy and don't want to look up point costs, I'll assume that they can all easily fit on a 1000 point team. So normally, this team starts with 10 actions.

Also, for argument's sake, the team consists of an extra Aquaman and an extra Chief.

So we've got 6 Leadership rolls that can be made. Incredibly, all rolls result in a "6".

Namor rolls and uses his ability. I now have 12 actions total, 2 of which must go to Atlantis keyworded characters.

Attuma rolls and uses his ability. I now have 14 actions total, 4 of which must go to Atlantis keyworded characters.

Both Chiefs roll and each one decides to add a Manipulate token to their card instead. (So I'm still at 14 actions, 4 of which must go to Atlantis characters)

Aquaman #1 rolls for Leadership. I get an extra action in my pool (now at a total of 15 actions, 4 of which must go to Atlantis characters)

Aquaman #2 rolls. I do not get to add any more actions to my pool from this, because Aquaman #1's action already maxed out what could go into the action pool.

Of course, none of these matter. After rolling six 6s in a row, my judge points out hat I'm using a loaded die and has me escorted to he parking lot where he and the other players do very bad things to me in retribution....

Thanks a lot !