A simplified approach using some ES6 methods.
/*!
* Get all siblings of an element
* (c) 2021 Chris Ferdinandi, MIT License, https://gomakethings.com
* @param {Node} elem The element
* @return {Array} The siblings
*/
function getSiblings (elem) {
return Array.from(elem.parentNode.children).filter(function (sibling) {
return sibling !== elem;
});
}