They could be sent to federal prison and fined if convicted.
The grand jury alleges Morgan, a Democrat, accepted more than $400,000 in illegal payments from three companies to use his position in the Senate to help them. Grand jurors allege Martin and Skeith conspired with him to help two of the companies.
The grand jury said payments mailed to Morgan were disguised as checks for his legal services.
Ogle has said Morgan, an attorney, was paid for legitimate legal work, including assistance with litigation.
Ogle also has described the investigation and indictment of Morgan as politically motivated. U.S. Attorney Sandy Coats called that claim absurd.
Morgan was Senate president pro tempore or co-president pro tempore from March 2005 until November 2008, according to the indictment.