The more complicated the family and the more people involved in the business, the more likely there are to be fights. Actually, scratch that. No matter how few people or how little money is invested, there are bound to be fights. If you're starting a family business, you should know that disagreements are in your future, sure as tax season and the grave. Be prepared.
Have a procedure for dispute resolution staked out in advance, like a limited partnership agreement that allows for settlement through professional mediation. It's even possible to discourage abuse by structuring the agreement so that the losing party is responsible for the cost of mediation.