Advice on sexing JG chicks, please?

My splash Jersey Giant chicks are now 7 weeks old and I would like to know how to sex them.

The only noticeable difference is that since their feet have turned from pinkish to grey 2 of them have yellower soles than the 3rd, which has just got very pale grey soles. I'm hoping that's not 2 boys & 1 girl   

Oh I do hope it's the right way round. The darkest & lightest ones (the ones with yellower soles) feathered up much quicker than the middle coloured one, who I thought looked quite scraggy compared to the other two for a couple of weeks.

I can cope with one boy, but not two, as I've already got one young lad...