The in-laws are family by treaty — kin acquired through the vow, the other tribe now yours by marriage. Dream in-laws negotiate the merged systems: whose customs at whose table, and the approval that marriage did not automatically include.
Positive Resonance
The tribes merged workably, kin gained by choice's treaty
Shadow Aspect
Approval perpetually pending, customs at war over holidays
Nuances
Meeting them: the treaty's first summit
The approving nod: acceptance into the acquired tribe