Why had st. john, diana, and mary's father quarreled with their uncle john?

I believe the answer is: Their father quarreled with their Uncle John over a business proposition that was speculative and brought ruin to their father.

Because of this, resentment toward their uncle started to built up because they perceive their uncle as the main source of their problem. ( even though it may not fully the uncle's fault since the business proposition is speculative in nature, this mean that it has a high level of risk in the first place.)