selrirspe lujvo

x1 is the spouse of the child/offspring/protegé of x2 by standard/law/custom x3.

Son–/daughter-in-law. This does not mean "child bride" in the sense of a juvenile who is wed; use "verba speni" for such purpose. Compare to: "rirspe", "sperirni", and "speselrirni".

In notes:

x1 is a daughter-in-law/son-in-law (a spouse of a child of) of x2 according to law/custom x3.
x1 is the parent-/mother-/father-in-law (parent of spouse) of x2 according to custom/law x3.