Ellefson was waived by the Jaguars. He had one catch for 10 yards as an undrafted rookie in 2020.
Holmes had 43 tackles and a sack for the Vikings after joining the team as a 2018 fourth-round pick.
In addition to Ellefson and Herndon, the Vikings have also added a tight end to the practice squad. Zach Davidson joins running back Ameer Abdullah, tackle Zack Bailey, fullback Jake Bargas, linebacker Tuf Borland, safety Myles Dorn, guard Dakota Dozier, guard Kyle Hinton, wide receiver Myron Mitchell, cornerback Parry Nickerson, wide receiver Whop Philyor, running back A.J. Rose Jr, cornerback Tye Smith, and defensive end Kenny Willekes.