The chicks are mixes/crosses. Sexing by appearance is out. Sorry.
What you're going to have to do is simply wait. At six weeks? The cockerels will show themselves with bright red combs and wattles sprouting. The pullets will not sprout much of anything until 12 or 13 weeks. Sexing will...
ISA Browns are sex links. No need for guessing at wing feathers, just look at the chicks. White/yellow are cockerels and buff/brown/red chicks are pullets. But, since these chicks are a mix, all bets are off.
As said earlier, unless a slow feathering line is bred to a fast feathering line...