Agree with above points. It sounds like it should have been dealt with a long time ago. Being this close to vesting is the cost of inaction. The equity issue feels like a sunk cost at this point.
Would initiate a conversation around performance to set expectations that performance needs to improve or their position is at risk.
Be the hero of the story: treat the employee fairly and raise performance expectations. Hopefully, the equity is a small price to pay.
Ha! 26. I sympathise - but have to admit, I am quite excited for this! I just know there are going to be so many interesting people there, doing so many interesting things!