Seay redshirted in 2011 and was one of the final members of Georgia's so-called "Dream Team" signing class that year. He was not immediately available for comment.
Marshall played on special teams and was set to play basketball, but had not joined that team for a game so far this season.
Sanders redshirted due to shoulder surgery after appearing in three games in 2011. Reasons for his dismissal are unknown, but he was not involved in the incident with Seay and Marshall, according to a source.
"It's a privilege to play college football and to be a part of this team and University," coach Mark Richt said. "Along with that privilege comes certain responsibilities. Mistakes were made and part of our job is helping them learn from mistakes. Going forward, we are committed to assisting them find opportunities where they can continue their education."