What about three first names? Does the third one cancel out the second, or is the effect cumulative?

“Von” isn’t a first name, it’s German for of/from. Same with the Dutch “Van”, the Italian “da”, the French “de” (though that one might mean "the ", I’m not sure) and several other examples from different languages

The Thomas family in my town always names their first son Thomas.

Thomas Thomas the fifth is the most recent heir to this sobriquet.