I'm not in anywhere near as stressful a situation (just a team leader), but what can help is making sure that each thing that needs to be done is in a JIRA tick

I'm not in anywhere near as stressful a situation (just a team leader), but what can help is making sure that each thing that needs to be done is in a JIRA ticket (or sticky note, or whatever you use) with a good description. Then it has the potential to be assigned to anyone in your team: cofounder or otherwise. It also means it is recorded, and you can have meetings to discuss priorities. Chuck it in the backlog or the "next month" bucket or get rid of it entirely, or do it right now. Anything that slips through because you decided it was a lower priority you have to let it go. It might come back to bite you but you only have X resources.