I don't know much about any of these guys except Thornhill.
He was a durable three-year starter at Virginia. He played corner his second and third years and moved to safety as a senior. An explosive athlete with good size, great speed and a real nose for the ball, Juan is excellent in coverage and is an aggressive tackler, and while he excelled at safety I think his best position as a pro may be slot corner--the tall, long prototype Chris Richards looks for. He's a smart player who seems to adapt and learn fast. He improved every year at UVA and as a senior compiled 98 tackles and 6 INTs. I think he would start somewhere as a rookie in Dallas and have an impact no matter where that is.
BTW, it blows me away that Olamide Zaccheaus didn't get a combine invite. He's also a three-year starter who began his career at RB and played 12 games as a freshman. He led the ACC in receptions in 2018 with 93 and totaled 1058 yards and 9 TD on the season. He's #2 all-time in receptions in the conference and #20 all-time in TDs. At 5'8" 190, the former RB has great quickness and great hands and is a spectacular runner after the catch. It'll be interesting to see what he does at his pro day but all he did in Charlottesville was get open and move the chains. He's a bigger, faster Bease with real running skills, and I'd LOVE to see him in Dallas.