Did the faith of the Old Gods allow for multiple wives? It’s seems like Garland the Bridegroom had multiple wives before he married Lymond Hightower’s daughter. Would they have been “wive” wives? Or would there have been one main wife and several concubines, sort of like what the Ironborn have with their Rock Wife and Salt Wives.

We don’t have any evidence of how these marriages were thought of on the mainland – to be honest, we barely have any evidence of multiple wives to begin with – so I don’t know. If I had to guess, I would say that there would probably be a complex social hierarchy, with seniority and the influence of the wife’s family among the factors involved. 

Another interesting question is how this interacted with primogeniture, because the two practices don’t combine easily. My guess is that, unless the first marriage was childless, subsequent marriages were more likely to be with younger daughters and/or from more juniior families, as the wife’s family isn’t getting long-term influence with the next lord but rather only short-term influence with the current lord.