How do I leave the business to one child and treat the others fairly?

By separating the business from the arithmetic. Dividing everything in thirds usually forces a sale nobody wanted.

One child works in the business. Two do not. An estate plan that divides everything equally seems like the fair answer and frequently produces the outcome nobody wanted: a forced sale, because the only way to give three children a third each of an illiquid company is to turn it into money.

The child who spent fifteen years building it loses their livelihood. The other two receive a third of a distress sale. Everyone is worse off, and the plan did exactly what it said.

Separate the business from the arithmetic

The alternative is to transfer the operating company to the child inside it, and equalize the others outside the entity. Fairness is achieved in the estate as a whole rather than inside each asset.

What does the equalizing:

• Other assets. The house, investments, retirement accounts. Often enough on its own if the business is not the whole estate.
• Life insurance. The cleanest tool for this. A policy sized to the gap creates liquidity at exactly the moment it is needed, and it is money that was never inside the company to begin with.
• A note. The child taking the business buys out the shortfall over years. Workable, and it leaves siblings as creditors of a sibling, which is worth thinking about carefully.

Consider transferring during life

There are advantages to moving ownership over time rather than at death: the successor is established while the founder can still support them, the transfer can be made in increments, and growth after the transfer sits outside the founder's estate. It also lets everyone see whether the successor can actually run it, while there is still time to change course.

Fair is not the same as equal

Be explicit about which one you are aiming at, because a family that has not discussed it will assume equal and be surprised. Some founders deliberately give the operating child less overall, on the basis that they are receiving the thing they wanted. Some give them more, on the basis that they built it. Both are defensible. Neither survives being discovered for the first time after the funeral.

Say it while you are here

The single best predictor of whether this works is whether the founder explained it themselves, in a room with all three children in it. The drafting is the easier half.