Is constantly wearing bracelets, based on the advice of elders and a belief that not doing so diminishes the husband's life, considered a superstition that contradicts Islam?

Islam dictates that Allah ordained the lifespans and provisions of all creatures before their creation and while they were in their mothers' wombs, and this ordination does not change. Supplication is one of the greatest means of attaining what is sought, but it does not alter predetermined lifespans or provisions.

As for bracelets worn with the intention of prolonging life, or attracting benefit, or repelling harm, they are forbidden and are considered "amulets" associated with polytheism (shirk). It is not permissible to obey anyone in an act of disobedience to Allah. However, one should be gentle in explaining the Shariah ruling to whoever commands such an act and seek the husband's assistance.