My question is: did he renounce the said titles and succession rights for his descendants as well -- including those from his previous marriage? That would not have been justified, since his first wife (Infanta Maria Teresa of Spain) was clearly of equal birth. As I understand, she and her children were all German (as well as Spanish) royals: I believe they were all styled with the title Prince(ss) of Bavaria, with the qualification of Royal Highness.
Just when and how did Ferdinand's children forfeit their dynastic membership in the house of Wittelsbach? I see that even his sons were excluded from the line of succession to the Bavarian throne, as of 1918 (when the German monarchy got abolished and the Bavarian royal house was deposed).
Of course, they remained dynastic members of the royal house of Bourbon, retaining their Spanish succession rights. All were styled with the title Infante/Infanta of Spain, with the qualification of Royal Highness. But today, not even Ferdinand's male-line descendants are styled as princesses of Bavaria (only females remain: his elder son never married; although his younger son married and fathered two sons, only the elder of those married. The said elder son, now deceased, married but fathered only one child -- a daughter).
In official genealogies, I see that Ferdinand's grandchildren through Infante Josť Eugenio (who married a Spanish noblewoman) and great-granddaughter through Josť Eugenio's son (who like his father married a Spanish noblewoman) are all styled with noble, but not royal, titles. As male-line descendants of King Ludwig I of Bavaria, however, they have "Baviera" in their names.
Of course, the Spanish naming system being what it is, a child adopts both his father's and mother's surnames. As it was, Josť Eugenio's daughters also married into the nobility: his grandchildren through them, then, have "Baviera" as a secondary name, whereas his granddaughter through his son has "Baviera" as a primary name (just like her aunts).
One would think, however, that in light of the house of Wittelsbach today having done away with all marital standards (with no requirement that dynastic members marry only royalty), these male-line descendants of Ferdinand might bear Bavarian royal titles, whatever might be said about succession rights (yes, I know that it's in the male-line only) ...