The court would likely accept the letter for purposes of calculating child care expenses. It is somewhat problematic that it is from your father because one could easily get a family member to write such a letter. If the court feels that the amount you are paying is not unreasonable (and it doesn't appear to be), then it shouldn't be a problem. Note, however, that if the matter is not settled and there is a trial, the letter would probably not be admitted into evidence. Your father would likely have to come in and testify and be subject to cross-examination.
Depends on the court. They may if it is Family Court.
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