Simply, to mean "have to" (or must), in esperanto you say "devi". "Havi" only means the idea of possession (materially or abstracly) as said by Pauchjo. For example to take the same words: "Ili havas laboron" means "They have (own) a job"
"Need" and "have to" are synonyms. Why does Esperanto have two words for this, when there are no nuances between them? It seems odd for a calculated language to have redundancies.
Actually, I take this back. Have to is a phrase synonymous with must, which concerns obligation rather than need. I return to having no issues with Esperanto.