Getting next sibling element using XPath and Selenium for Java

Use following-sibling axis :

WebElement followingSibling = child.findElement(By.xpath("following-sibling::*"));

List of available axes by MDN, for further reference : Mozilla Developer Network : Axes

WebElement parent = child.findElement(By.xpath("following-sibling::*[X]"));

X will be the Xth sibling of that element.