We've had two husband/wife teams. One is currently with us is a demorlizing circus act. A previous husband/wife team were in mgt positions and created tons of their own damage, thankfully after the wife left, the husband has behaved himself. I think that husband/wife teams can feed off each other in a negative way. Have you ever seen one work well? No....but I've seen several that worked badly.
When my wife and I got married (in 1996), she thought that maybe someday we'd have a company together. She now realizes what a horrible mistake that would make.
Nepotism rarely works well...though the excuses, rationalizations, etc. for it sometimes provide terrific humor after a few beers...
Kevin