In the OG prisoners dilemma, the best result was when both people choose the selfless act, the second best overall was if only one person did, but that was worse for the selfless one, and the worst option overall was if both people acted selfishly, but it was better for the person who would have acted selflessly.

Something like:

• both one year of prison if no one talks.
• if one person talks, they get no years and the other guy gets 3
• if both talk, both get 2 years of prison.

So here it should be worst for you if you don't pull the lever but the other person does, but the best (least people die) scenario is if neither person pulls the lever and allows one loved one to die each. The incentive structure should be set up that no matter what your opponent does, acting selfishly will mean less of your loved ones die.

Maybe if you pull and the other person doesn't, their trolley also somehow kills its occupants? And it's two people per trolley and one person per track.