Use commas when there is only one such person because it’s redundant information; do not use commas when there is more than one such person; see also CMS 5.21. An example: Mary’s husband, John, and her son Greg went with her. In this example, Mary has only one husband, so his name is set off by commas: John is a “restatement” of husband. Mary has more than one son, so the commas with Greg are eliminated to show which son is being referred to specifically, from among the other possibilities. If she had only one son, his name would also be set off with commas.