Friendship is personal, business is professional. Make a partnership deed.Partnership is an agreement or contract between the partner in which everything is described, like profit sharing, investment, process and how to divide the profit sharing,terms and condition of the partnership and profit sharing, limit of drawing ( it is the money which we withdraw from the business for the personal use) etcRemember without partnership deed any kind of business which is run by the two, is illegal and cannt be claim in the court Its better you refer the lawyer
As for as a family business is concerend, avoid an outsider into it. It can create lot of problems for you and your family members and there are chances the relationship between you and your family members as well as with your freind get spoiled and i am on the side it is an immature decision. If all of you are busy, consider giving him an employment and give him a good salary. If he is not agreeable to this, consider hiring a person from outside.Business decisions should come from your head and not from your heart.Anyway if you are still want to get him to your business as a parter, a partnership deed has to be made with the help of a lawyer. Please remeber in mind, as per Partnership Act, all the members are severally and jointly liable for any liabilities created out of Partnership. In the real world, what happens in such situation is the outsider creates lot of liability in the name of the Partnership and when it come to the point of payment he claims that he doesnt have the resources to pay and eventually all the other partners got attached to the liability.These are the possibilities. Take your own decision.