What do you suggest?

A If you put a team together, you are acknowledging that their work is group work; there is a conflict between the need to reward good work, not bad, and the simultaneous need to recognise that a team is an inter-dependent group you have set up for this specific project, and acted as one.

Split the 40k. With 20, reward everyone visibly and equally (percentage of salary).

This reinforces that it was a team effort. Those who didn't pull their weight will gradually feel the wrath of those that did and this may have an energising effect for next time.

With the other half, give those who worked on the team some individual projects to do and reward success accordingly. Don't make individuals on teams compete for monetary rewards; if they are good, they will compete for intrinsic rewards and long-term recognition. If they aren't, let their project team highlight this and then manage that through the performance management system and appraisals and thereafter reward withdrawal, perhaps.