Here is a Q&A example from the great Feargal Quinn on how to overcome conflict in Family Business: 

Question:   

My brother and I are involved in business together. My role is less active than his, however, we have had ongoing disputes about the direction the business should be taken and we are now barely talking. Have you any ideas on how we might resolve the situation?

Answer:    

Animosity among family members within a business can sometimes be disastrous as it tends to spread into the family and suddenly instead of two business people making decisions and debating a matter, the whole extended family end up taking sides and volunteering opinions.

My first piece of advice would be that if this is to be resolved, you both need to agree that whatever happens within the business, stays within the business and is not communicated within the wider family, otherwise you risk the splitting of the family down the middle with potential lifetime conflict.

Once you have achieved this you now need to focus on the business issue. Treat it as if you are not brother and sister, but rather two investors in the same business.

Your conflict seems to arise over decisions which are taken and direction the business is moving in.

It might be a good idea to get a third party adviser/mentor to come in and review the business without giving them any particular background and see what their recommendations are. This might help both sides to take a more neutral approach. It would also be a good idea if you both sit down and write down the areas of disagreement and then logically talk through each one and get agreement on how to proceed forward.

Running a business with a sibling is all about respect and using commercial logic to create a sustainable future. If the respect is lost, then you have no choice for one of you to buy the other out of the business.

Source:

http://www.independent.ie/business/small-business/advice-centre/problem-solver-oh-brother-we-have-sibling-issues-in-our-business-31514713.html