Question about being a financial sponsor for prospective student

Hello,

I’m being asked to fill out a letter indicating our intent to financially sponsor my SIL while she is a student in Japan. We are also being asked to provide records indicating our total savings and more. We are being asked to do this on behalf of my mother and father in law because they lack the sufficient savings, but they have told us we won’t actually be forced to pay and they will take care of everything.

How on the hook am I if my SIL needs money that my in laws can’t provide? Is this letter enforceable and can it affect my credit?

Thanks.