WASHINGTON — Three relatives of Americans the authorities said were killed by immigrants living in the United States illegally will attend President Trump’s first address before Congress on Tuesday, signaling his plans to showcase his administration’s early efforts to crack down on immigration as a security issue.

Jamiel Shaw Sr., whose son was shot and killed in 2008 by a man who was in the country illegally, will be among the six guests sitting with the first lady, Melania Trump, during the speech. Mr. Shaw became one of the most vocal advocates of Mr. Trump’s tough stance on immigration during his presidential run, appearing in a television ad on his behalf and giving a prime time speech at the Republican National Convention.

Mrs. Trump will also be joined by Jessica Davis and Susan Oliver, the widows of two California law enforcement officers who, officials have said, were killed by a Mexican immigrant who was also in the country illegally. The officers, Michael Davis Jr. and Danny Oliver, were shot and killed in 2014.

The release of Mr. Trump’s guest list comes as the president prepares to argue that, despite serious accusations about his administration’s relationship with Russia, the botched rollout of a travel ban with seven majority Muslim nations and other problems, he is following through on crucial campaign promises, particularly on illegal immigration and national security.

The president’s guests at a joint session of Congress typically reflect the administration’s priorities. Presidents often refer to their guests during their addresses, sometimes using their personal stories to illustrate their points.

Mr. Shaw’s son, Jamiel Shaw Jr., was a high school football star in Los Angeles and just 17 at the time of his death. He was on his way home from a shopping mall when he was shot twice by Pedro Espinoza, 19, who was a member of a notorious street gang and had entered the United States illegally from Mexico. Mr. Espinoza had previously been convicted of weapons possession and resisting arrest, and he was released from jail the day before he killed Mr. Shaw. He was…