Name the impact without exaggerating it
Describe who had to wait, worry, redo work, spend money, or make a choice with incomplete information. For a message about how to decline a family caregiving request, use this factual base: acknowledge what was requested, any real timing issue, and whether your answer applies only now or more broadly.
Make repair practical
Offer the repair you can actually complete, with ownership, timing, and any limit stated honestly. Give a direct no, a limited alternative only if you mean it, and any practical information they still need. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Let future behavior carry the proof
Do not overexplain private details, blame another person, or say maybe when the answer is no. When pressure, coercion, or retaliation is possible, use a safer channel and involve appropriate support. A promise inside a message is weaker than a visible change in what you do after it.