A will is a good instrument with a narrow job: it says who owns what once you no longer do. Families tend to assume it does more. In our experience the disputes that follow are rarely about ownership, because ownership is the one part that was written down. They are about timing, about the house, and about the difference between what was fair and what was equal.
The house is almost always the centre of it. It is illiquid, it is loved unevenly, and it is usually the largest single line. A document that divides it into equal shares has answered a legal question and created a practical one: three people now jointly own a building that one of them lives in. That conversation is much cheaper to have while everyone can still take part in it.
Timing is the second gap. A will transfers everything at once, at a moment nobody chooses, to people who may be at very different points in their own lives. Trust structures exist largely to reintroduce the element a will removes — the ability to say when, and under what conditions, rather than only who.
None of that is a criticism of the instrument. It is an argument for treating the will as the last page rather than the whole document, and for writing the earlier pages — the letter of intent, the note explaining why the split is uneven, the list of where things actually are — while they can still be discussed with the person who meant them.