You didn't "offer" them 30%, you started the company with them and when it came time to execute a partnership agreement – which has to be done early to avoid ac

You didn't "offer" them 30%, you started the company with them and when it came time to execute a partnership agreement – which has to be done early to avoid accidental general partnership – that's what was agreed on, based on shared expectations of future contributions. Now they have decided to prioritize other projects – but there is no way under US law to adjust their ownership without their agreement. It does seem like a vesting schedule for the founders would be better – but defining the terms of participation, and enforcing them, is difficult. Still, the performing partners would at least have grounds to sue, and that threat might be effective.