Do creole languages have one “base language” or two “parent languages”?

It’s a very good question.

Normally, creoles and pidgins are put in the too hard basket of linguistic family trees for precisely that reason. It’s very hard to argue for a single parent language, as pidgins, and the creoles that arise from them, really are mixed languages, with grammar from the one, vocabulary from the other, and structures from the lowest common denominator. So people are reluctant to say Tok Pisin is either Austronesian or Germanic; they typically put it in a category of its own.

A further complication is that there is almost always a single acrolect (“White”) parent, with the possible exception of Bislama; but any number of basilect (“Black”) parents. Pidgins typically arose in plantations, where slaves or workers spoke a lot of different languages and were torn from their social context. So adopting a pidgin was a matter of necessity.

Linguists tend to dodge the question, and creoles are so distinct from both basilects and acrolects, not to mention so much more similar to each other, that the question is not really that useful. But Multiple Parents is certainly closer to the truth than Single Parent.