Working with relatives or wife/husband might look a very smart thing. But think if/when things go wrong, then is not only the professional life paying the problem.... So, my suggestion is to learn treat relatives as a 'normal' collaborator, in order to avoid approaching in a wrong way the business goals, where you are forces to let go something that you wouldn't accept from anyone else.
My personal mistake was to do the first business as it was a big enterprise. I calculated / re-calculated everything 1000 times, was trying to make everything perfect, hired hundreds of useless people etc. And at the end of the day, I realize that the idea itself was not good enough and it would be better to avoid all this extra work. That is why it's better done than perfect;)
I shut down my last startup startup and I
feel shameful while writing this answer.
Here are the Startup Sins I committed with the wonder of bullet points: