so yours are much the same age as my oldest ones.
The stags I can see easily, they are taller, wider have bigger stronger legs and heads, have a bit rougher feathering and are starting to get their snoods.
The hens are smaller and petit, with thin short legs and a lovely rounded shape but theres one hen thats slightly bigger than the rest and it has a big bigger head which is slightly more stag shaped than the rest.
I'm 90% sure she's a hen but I keep looking at her

There's definitely a bit of Fatima Whitbread about her... she looks like a girl but you wouldn't risk finding out!

yes they can be vent sexed at day old but its not 100% guaranteed
Although i'd like to think they would do better than 3 out of 5 right, that ratio is more like unsexed birds.
Have you any pics of them?