If you do not sign, the employer still have the right for

the patents. you have nothing to loss or gain. If you signed, at most you have nothing to loss. You may have a chance to gain.

If you have evidence that $2000 for each inventor, you can request to this amount.

My understanding is that the bonus is a kind of compensation for employee's work, no matter paid now or later. Therefore you can request to be compensated for your work.

If they do not, what can you do? ( up to you to make a decision)