V.H.
20 mins a LB plus 20 mins over so for the 3LB breasts thats about 80 mins if you do them all at the same time. Put a bit of butter on them and season with pepper. Add some poatoes in a little olive oil and you will have roast spuds too since they take about 80 mins to do too!! You will only need about 1/2 LB meat per person - imagine a steak at about 8oz per person - with all the trimmings that is A LOT of meat!
Good luck!