Federal investigators are examining financial transactions involving Paul Manafort and his son-in-law, who embarked on a series of real estate deals in recent years fueled by millions of dollars from Mr. Manafort, according to two people familiar with the matter.

The transactions involve the financing of apartments and luxury homes in New York and California using money from Mr. Manafort, as well as from other investors solicited by the son-in-law, Jeffrey Yohai, including the actor Dustin Hoffman and his son. F.B.I. agents have reviewed financial records related to Mr. Yohai, who has been accused in a lawsuit of defrauding investors, the sources said.

It was not clear if the F.B.I.’s interest was part of the broader investigation that has ensnared Mr. Manafort, who was President Trump’s campaign chairman until he resigned last August amid reports that he had received millions of dollars in off-the-book payments for his consulting work in Ukraine. Mr. Manafort has been the focus of several inquiries looking into his business activities, failure to file foreign lobbying disclosures and possible collusion between Trump campaign associates and Russia.

Mr. Manafort has emerged as a key figure in the F.B.I.’s Russia investigation, which has focused on interactions between Trump associates and Russians during and after last November’s presidential election. In addition to his work for Ukraine’s former president, an ally of the Russian leader Vladimir V. Putin, Mr. Manafort’s long lobbying and consulting career has included numerous financial dealings with Russian oligarchs. One of his former employees has been investigated in Ukraine on suspicion of having ties to Russian intelligence.