As this is all hypothetical, you left out the most important option: selling your soul to the devil. (i.e. the soul and the devil are hypothetical entities taken as being real for the purposes of this thread). All the other options are only limited in effect, selling your soul is everything. You could say killing someone else is selling your soul, but it's not an explicit pact of giving away your Self with the dark one, it's merely a permanent scar which can never be healed or erased.
I could not kill someone else (being an innocent 3rd party) to save another (or myself). Basically it's a losing calculus to do it. You might think it's a zero sum game (might as well have the person you don't know / know the least die because someone's going to die anyway), but the long term emotional and psychological outcome is worse if you do the killing, instead of the sadistic psychopath doing the killing. I'd be willing to lose a body part or suffer for another, just don't ask me to do the cutting, I'd even do it for a total stranger if it meant my hand vs. their life. Actually, if the maniac tries to lay the burden of decision on me by saying I get to decide whether I die or some other person dies then I'd choose to die every time, regardles of who the other person is. Or rather I would hope I had the courage to follow what I think is the right thing to do. If it's between my loved one and the psycho-maniac who is putting my loved one in a life threatening situation then the psycho-maniac will lose every time.
Ultimately it's not love for another that would motivate me, it's love for myself. I love myself too much to allow myself to be an agent of misery to another innocent party. I would rather suffer the anguish of losing a loved one by my own choice than cause others to suffer exactly the same anguish of losing a loved one when they had no say in the matter.
Even considering the scenario where there is no psycho maniac trying to manipulate your morality e.g. an accident scene with 2 people trapped in a car that's sinking under water . One is someone you love the other is someone you don't know / don't know well. My instinct would be to save the one I love. But if I had time to consider it I would first save the other, then hope there was time to save the one I love. Again I would rather suffer through my actions than cause someone else to suffer through my actions. I think the happiness created in the loved ones of the person I save would be greater than the grief suffered by myself and others at the loss of the one I love.
Of course this attitude is helped by the fact that I don't believe physical death is the end, only a transition.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix