Defense Secretary Pete Hegseth shared detailed information about forthcoming strikes in Yemen on March 15 in a private Signal group chat that included his wife, brother and personal lawyer, according to four people with knowledge of the chat.

Some of those people said that the information Mr. Hegseth shared on the Signal chat included the flight schedules for the F/A-18 Hornets targeting the Houthis in Yemen — essentially the same attack plans that he shared on a separate Signal chat the same day that mistakenly included the editor of The Atlantic.

Mr. Hegseth’s wife, Jennifer, a former Fox News producer, is not a Defense Department employee, but she has traveled with him overseas and drawn criticism for accompanying her husband to sensitive meetings with foreign leaders.

Mr. Hegseth’s brother Phil and Tim Parlatore, who continues to serve as his personal lawyer, both have jobs in the Pentagon, but it is not clear why either would need to know about upcoming military strikes aimed at the Houthis in Yemen.

The previously unreported existence of a second Signal chat in which Mr. Hegseth shared highly sensitive military information is the latest in a series of developments that have put his management and judgment under scrutiny.

Unlike the chat in which The Atlantic was mistakenly included, the newly revealed one was created by Mr. Hegseth. It included his wife and about a dozen other people from his personal and professional inner circle in January, before his confirmation as defense secretary, and was named “Defense | Team Huddle,” the people familiar with the chat said. He used his private phone, rather than his government one, to access the Signal chat.