Responsa על כתובות 98:10

Q. A was survived by his wife, a married daughter, and a single daughter. Subsequently the married daughter died and then her death was followed by that of her mother. The latter had not taken the required oath regarding her ketubah. The unmarried daughter took possession of A's entire estate; but, A's son-in-law demanded half of the estate on the grounds that his wife had been entitled to it, and that he was her rightful heir.
A. As long as A's widow did not take an oath regarding her ketubah, A's entire estate belonged to his two daughters. A's son-in-law, being his wife's rightful heir, is, therefore, entitled to half of A's estate.
This Responsum was addressed to Rabbi Menahem.
SOURCES: L. 226; Mord. Sheb. 780. Cf. Israel Bruno, Responsa 21.