I have been in a couple situations like this. Twice, sadly, was with my family members. In those cases I obviously had a "side" so it was a little different.
Anything else I have said that I am happy to provide any paper work to BOTH parents (two copies of everything, even if only one parent asks for it) Receipts are only with the person who paid and I do not issue replacements if they are lost.
It's all about how much your are comfortable with.

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