They don't have agents (at least not legally) . They can't work out for teams or anything like that. Right now, they just submit paperwork essentially saying they are thinking about it and then get a report detailing where people who know the NFL (GMs and personnel directors) think they might be drafted and a critique. If they officially declare for the draft next month they become ineligible. Invites for the combine only go to people officially in the draft.
I have no actual information whether Shell will be on the team next year. If he graduates he could play DI next year without sitting out. If he's not graduating he can only transfer down and have eligibility to play next season. He can't sit out a year because next year will be his 5th. I don't know what he is thinking but I don't think he has a chance of even sniffing the draft in April. His best chance for 2017 would probably be if Smallwood does leave and he gets to show he has dramatically improved.
Worley is not an NFL level corner. He'd be better in college at safety because he lacks elite corner speed, agility and balance. He could not play corner in the NFL. In terms of getting drafted, his best prospect probably would be for 2017, if he played safety for us and did well. I doubt that happens as we are thin at corner and he's the only one coming back with much experience. I don't see Worley as a guy anyone would view as having such elite athleticism that he'd get drafted as a project.
Smallwood is the one who has the hardest decision. If he's told he's a late round selection, he has to give it a lot of consideration. Unless he is told he could substantially improve his stock by improving on something it is possible to improve (skills such as blocking, receiving, etc.) as opposed to being told he's a late round guy because of physical traits -- his size and speed, which are not going to change significantly no matter how hard he works-- he has to think hard about spending an extra year of his limited career in the NFL.