Serpents/brittles ---> yes in nearly all tank sizes and without need, specifically, for a reef tank (however certain predators will eat them; the green is a possible predator of small fish; and the bright red large one should go into a mature (6 month) old stable reef tank).
Linckia are good but hard to care for. They ALL require very pristine reef tanks with a lot of LR, since, as mentioned, they can not be spot fed. A blue Linckia, IMO, should not go in a system under 100g minimum.
An orange, burgundy, red or purple might be suitable for smaller tanks (55g-100g) but still need a LOT of LR and it is best to only keep one. They take about a year to starve, so it is hard to tell how they are doing. All need, as mentioned, long acclimations for the most part. Research needs to be done before purchase on this aspect.
For tanks under 55g (to about 29g), only a Linckia multiflora is suitable, IMO.