Agreed, at least regarding the Young twins. The Sahlmans, especially Colin (although Aaron's 1:48 800m suggests he has similar bottom-end speed), have demonstrated superior natural speed and have longer legs/strides, which bodes well for development at the next level, i.e. kicking off a fast pace, superior speed endurance, etc.
Leo has some speed, but Lex seems to run all out from the gun. I think you hit the nail on the head: They're A-tier talent with S-tier training through high school; Nico probably something like S and B+, respectively, which would explain why Leo and Lex may run faster PRs in high school, but I'd bet that they won't come close to what Nico is doing now on the track.
As much as I'm rooting for their success, objectively speaking, I think the Young twins will hit a wall rather early. I'd love to be proven wrong, though. Or maybe their true event is the 10k, who knows.