Since you didn't specify the size of the island, the climate, the plant coverage, the soil quality, and fishing conditions in surrounding waters, I can only comment on what I'd guess would happen socially.
About ~10 of the incels would barely even talk with the others and mostly keep to themselves. Most of the other half would be relatively benign with their social interactions but quickly start hating each other's guts because of disagreements over random bullshit and social maladaptation. One or two hideous (because they wouldn't be incels if they weren't that ugly) alphas would emerge and relentlessly bully the non-shy half and dominate the shy half. These would quickly become the de-facto leaders of the group. The success of the group's survival would depend largely on the competence of its leaders. Also, ~5 of them would discover their latent homosexual tendencies.