Why does this keep coming back?
The argument that repeats is usually two different arguments wearing one costume. How to find the one underneath, and what to do when it turns out to be a real disagreement rather than a misunderstanding.
How do I say no and not blow this up?
A boundary is a statement about what you will do, not an instruction about what they must do. Why that distinction does most of the work, and how to hold one when the first reaction is not a good one.
How do I say sorry so it actually lands?
What a real apology contains, the three versions that make things worse, when to wait, and what to do when it is not accepted.
How do we do this without it becoming a fight?
Money arguments are rarely arithmetic. Separating the facts conversation from the fairness conversation, and writing down what you actually agreed.
How do I keep this civil when it is not?
Short, factual, one topic at a time, and written as if it will be read by somebody else one day — because it may be. Including what not to do with the children in the middle.
How do I raise this without damaging myself?
Work conversations have an audience, a record and a power difference. How to decide what you are actually asking for, and what to put in writing afterwards.
How do I bring this up without living in an atmosphere?
Small things compound. Raising it while it is still boring, asking for a specific change rather than a different person, and running a house conversation that ends in decisions.