Well, it was more complicated than that. In 1695, when it was clear that Charles II wasn't going to have an heir, three parties were created within the Court:
1. Mariana of Austria, the Queen Mother, was the "leader" of one of them which supported her own great-grandson Joseph Ferdinand of Bavaria as the rightful heir. If the renunciation of infantas Ana Mauricia and María Teresa were legal, then it was really Joseph Ferdinand who should become King of Spain. María Antonia could have renounced in Austria to her Spanish claim, but without Charles's approval this renounce was invalid.
2. Mariana of Neuburg, the Queen Consort, was the "leader" of a second party which supported her own nephew, Archduke Charles of Austria (son of Emperor Leopold and Eleanor of Neuburg) as the rightful King. This party had Ana Mauricia, María Teresa and María Antonia's renunciations as legitimate. So the next in line was Archduke Joseph, but as he was heir of the Empire, the claim fell on his younger brother, Charles.
3. Cardinal Portocarrero, the most important advisor of King Carlos, supported the Duke of Anjou, Philip of Bourbon, grandson of Louis XIV and infanta - and former Princess of the Asturias - María Teresa. This party thought that Ana Mauricia and María Teresa's renunciations were only legal in order to avoid the Freench and the Spanish Crowns joining together in a unique kingdom. So, the rightful heir of King Carlos was his grand nephew Anjou.
It was more a political issue than a family confilct, although it would end up in that - and then into a European war. In 1697 Carlos chose Joseph Ferdinand as his heir because his party and his claim were the less controversial. But the child died in 1699 and the Succession issue became even more complicated. Queen Mariana, realising that the Queen Mother was dead, thought she could easily convince Carlos into naming her nephew the Archduke as his heir. But Carlos chose Anjou because he thought it was the right thing to do, he thought a divine right couldn't be avoided by a human document. When he died in 1700, the two parties (in which other countries had become involved) were ready to fight. And they did...