Here are some pictures I have, all of them are full grown but it's important to note my light brahma is a fairly bad quality hatchery chicken and is a bit smaller than how big light brahma hens are supposed to be, the silkies stay quite small
They probably are too young to say, but my guess (which due to the age is barely better than just guessing so not accurate) the lighter one might be a cockerel and the darker one a pullet but you should post pictures when they are older
The 8 month old, definitely a girl, as for the 2 month olds I can't tell by those pictures, of possible could you get full body shots of them standing up (so I can see posture) and a picture of their combs