Black-winged Stilts can sometimes be difficult to age & sex, because there is a lot of variability in pattern.
Among your four birds, the easiest is the one on bottom right. The very black back indicates an adult male. The legs are fairly bright pink, again suggesting an adult. Males tend to have whiter heads, as seen on this bird.
The others are a bit trickier. Females have browner backs than males and usually more dark feathers on their heads. But first-winter birds also often share these features. Adults tend to have brighter legs than first-winter.
I think that the two at the top are first-winter, based on the browner upperparts and paler, slightly grey-tinged legs.
The bird at bottom left is very difficult, especially due to the distance. It seems fairly dark above and pink-legged. I think it is an adult female, but I'm not entirely sure.
