I went through something similar. I'm a cofounder at a small startup and had a difficult health scare with myself, my wife and both kids, all around the same time.
Ceritnaly no right answer, and it was hell at the time, but looking back, here's a few things:
My cofounder took care of my many shortcomings during that time, no questions asked. He also has a family (which may help in that mutual understanding) but he'd get tasks with no context and say "don't worry, I'm on it" and it just got done. I hope you can get to this point with your other founders.
Your startup is more resilient than you think. I missed many things during that time, respond badly to emails, missed calls and we came out the other end alive. I realized we weren't as fragile as I thought. Ironically some of those missed calls and poor emails still turned into customers. Your startup will be able to handle you making mistakes and being less involved when needed.
I took me a long time to get back to "normal". It felt like chaos for almost 9 months and at some point, it may feel like the chaos will never end. You need to know that it will get better and you will begin to feel sane, even though it may take a while.
This may controversial, but the family and startup are not mutually exclusive, so I never think of it in terms of balance. The fact that you started a company means you're probably happier there than at a large company, being happier makes you a better husband and father and family unit, and that family unit will be your support through the ups and downs of building a company.
Good luck, you can do it.