Well, one solution would be to use these -- e.g.
Orléans-Braganza -- whenever a royal is a dynastic member of two houses.

Indeed, given that royals have traditionally married within their own rank, most have been descendants of multiple houses. It's just that membership has largely been through the male line, whereas succession sometimes was permitted to or through females (the strict Salic law has been the exception, in European history).

Add to this the fact that both Spain and Portugal have always honored a person's maternal (as well as paternal) heritage: indeed, whether one is talking of royals or commoners, a child takes both his father's and mother's surnames. It's just that only the father's surname gets transmitted to his own children, later on.

The children of Prince Ferdinand of Bavaria and Infanta Maria Teresa of Spain were both Bourbons and Wittelsbachs. Because they never succeeded to either the throne of either kingdom, hyphenating the name of a dynasty never applied. But nothing changes the fact that they were dual dynasts, with membership and succession rights in both Spain and Bavaria.

Of course, they eventually forfeited the latter. But it's interesting to speculate on what would have happened, but for Ferdinand's renunciation -- or the theoretical (if only remotely possible) scenario of his children coming into a dual inheritance.

Perhaps Ferdinand was not made to renounce his Bavarian princely title and succession rights at his first marriage precisely because he had virtually NO chance of even inheriting the throne, anyway. And the hypothetical children born to him and his first wife, given their genealogical position, were just as unlikely to ever inherit the Spanish throne.

Infanta Maria Teresa's older sister, on the other hand, married a man who had closer succession rights in a non-reigning house -- not to mention the obvious fact that Infanta Maria de las Mercedes had a closer place in the line to the Spanish throne. As it was, her husband (Prince Carlo) was made to renounce his inheritance rights to the defunct kingdom of the Two Sicilies.

A renunciation which he thought meaningless, but which his descendants have made much ado about ...