We don't know much about the Sparrows just yet, but we can make some guesses about their abilities. We can safely assume that Ben retains his ability to summon monsters from other dimensions and manifest them through his body. Usually, we see that in the form of him sprouting giant tentacles from his body, but hopefully a third season will give us room to explore all the horrible beings he can call forth!
As for the rest of the Sparrows, in the comics their powers are as follows: Number One has super-strength (and looks just like Luther); the blob-looking sibling can self-mutilate and transmit the damage to any targets; another sibling can fire an energy blast from their face; another can transform into a murder of crows to attack people; and there's one who is just a floating cube that we would guess has some kind of telekinetic or mind-manipulation ability — because that's how it always goes with floating cubes, right? There are two other siblings whose abilities are still unknown, so we'll have to wait to figure them out in the comics or the series.