Responsa על כתובות 173:9

Q. A and his wife drew up a document for the benefit of her son (A's stepson), in which was written: "Give to our son…" Does the expression "our son" invalidate the document since the beneficiary is not A's son?
A. A person who brings up an orphan in his house is in the same position as the orphan's father. Therefore, the phrase "our son" is quite appropriate. Moreover, the phrase in the document "to our mother so and so the daughter of so and so"… referring to A's mother-in-law, does not invalidate that part of the document as long as the name of the mother-in-law is given. For the term "son" or "mother" is an affectionate expression correctly used in this sense even when such relationship does not exist.
SOURCES: L. 242; Tesh. Maim. to Mishpatim 48. Cf. Maharil, Responsa 81.

Q. R. Moses, the plaintiff, was not present when the defendants, the Jewish inhabitants of Quedlinburg, took an oath in order to nullify the testimony of R. Moses' single supporting witness; must they take the oath again in the presence of R. Moses?
A. If the oath has been legally administered by a proper person (who is related neither to R. Moses nor to the inhabitants of Quedlinburg) there is no need for another oath.
This Responsum is addressed to R. Shemariah, and is the second communication regarding this case.
SOURCES: Pr. 231; L. 382; Tesh. Maim. to Haflaah, 1. Cf. P. 514; Mord. Ket. 296–7.