Should a family business have a buy-sell agreement even if all the owners are related in Ontario?

Yes — being related doesn't remove the reasons a buy-sell agreement exists in the first place. Family relationships change over time: siblings fall out, a spouse who married into the family can end up holding shares after a death or divorce, and unequal expectations about who actually runs the business can turn into disputes no one planned for. A buy-sell agreement sets out, in advance, what happens to an owner's shares on death, disability, retirement, or a serious falling-out — who can buy them, how they're valued, and how the purchase is funded, often through life insurance.

Without one, a deceased owner's shares typically pass through their estate to whoever inherits under the will or on intestacy, which might be a family member with no role in or interest in the business, sitting alongside relatives who do. That mismatch is a common source of shareholder disputes. Putting a written agreement in place while everyone is getting along is far easier than negotiating one after a death or rift, and it gives every family member clarity about what their ownership is actually worth if they need to exit.