(my version) Even without it being a ship (it's not in my rewrite), oliver is legitimately the only person who would even consider giving marcus a chance at redemption (except for MAYBE tasha)
chase and bree would never trust him again. adam is not nearly as naive or trusting anymore (he actually fulfilled his growing up arc in my series) douglas would melt him down instantaneously (and have a crisis later) and leo has always hated that mf lol
kaz would take what marcus did extremely personally because of how protective he is of his friends. skylar, while being disallowed murdering on earth by the hero council would be fine with executing marcus on the spot (since that's what they did on caldera)
tasha COULD maybe feel some form of sadness for marcus. she's a mother at heart, and a mother to kids who were incredibly lost before she came into their lives. but her actual kids matter more to her than any empathy she could have for marcus and marcus has tried to hurt and kill them too many times for her to forgive
oliver is a more logical thinker than kaz or skylar. and he has a lot of empathy too. I feel like if he spoke to marcus he could build a rapport and a sense of care or pity. whether or not marcus is just manipulating him lol
oh also daniel would probably forgive marcus too lwk