Related for Gittin 1:7

If he wrote [in a contract] to financially support his wife's daughter [after his death], or his wife's son—behold, they are like creditors and take precedence over everyone else [like the people collecting the ketubah payments in the previous halakhah]. He shouldn't say to them: "Go and do work, and I will support you", but rather they [can merely] sit [idly] and are elligible for financial support. If he wrote to support his wife's daughter and she gave him a receipt [that she doesn't need this], he (sic!, should read "הימנה") does not have the power [to decide on behalf of her minor children that they shouldn't receive financial support], for they act for a minor's benefit but they do not act for a minor's disadvantage.