A parent of one's son- or daughter-in-law, that is, a parent-in-law of one's son or daughter.

plural of co-father-in-law

The father of one's son- or daughter-in-law; that is, the father-in-law of one's child, or, the father of one spouse in relation to the father of the other spouse; either of two or more men whose children marry each other, such as the father of a bride vis-à-vis the father of the groom.

(rare) One's spouse's sibling's spouse; either of two (or more) people who marry siblings, from the perspective of the other.

(uncommon) One's spouse's brother-in-law (one's spouse's sibling's husband), especially one's wife's sister's husband; either of two (or more) men who marry sisters, in relation to the other; the brother of one spouse in relation to the siblings of the other spouse.

(rare, nonstandard) the grandfather of one's grandson- or granddaughter-in-law; that is, the grandfather of one spouse in relation to the grandparents of the other spouse.

plural of co-mother-in-law

plural of co-brother-in-law

plural of co-sibling-in-law

plural of co-sister-in-law