Good quiz, chance for me to learn something. Does 'Lanzarote' mean 'Spear Throw?..... I think El Hierro means 'The Iron'...... La Palma ..... The Palm..... and I think Fuerte Ventura means 'Strong Fortune' or words to that effect. I don't know but does Gran Canaria mean 'Big Dog'?
El Hierro does mean “the iron”, but it's not of the same etymological origin. “Lanza” means spear, but “rote” doesn't mean anything and the origin of the name is unrelated to spears. The Spanish words “can” and “cánido” mean dog, but “Canaria” doesn't. Your translations of La Palma and Fuerteventura are correct.
Suggestions. Maybe have Las Palmas and FuertAventura as type-ins?