Lets line up skills. I'm going to list 12+ as + for my own purposes here.
+/6/+/+/11/7 4/4/2/5
+/7/+/+/11/8 4/5/6/3
11/7/+/9/11/8 5/4/1/1
8/7/9/9/8/6 6/2/2/7
The 18 year old to me is worth keeping, if for no other reason than to evade the high purchase period that we have coming up in a week or so on the 18 year olds, in which he'd be 19. In addition, he already has the high SB and decent IS. ID will need to increase a few times, but he has time.
The 2nd player to me isn't worth much. He needs to gain a few IS to be a player. the IS difference of 4 versus 8 to me is almost a 10% jump in D.IV, and probably 4-5% there on. He'll be 22, that'll be a lot of time. You can just play him as a guard while you train inside skills.
The 1st players potential is his major letdown. I don't think much of 6 potential guys as long term options. On top of that, he needs 3-4 IS soon.
The 3rd player has higher potential, but SB'ing is less than desired, he'd have to almost be a PG.
The key factor here is you have 3 guys at 6 potential. Guys like this require better secondaries than what they have now because they cap out so much earlier.