1 will be fine by itself. If these are BB turkeys then you will be butchering it by the end next month if you want it 10 lbs. If they are heritage birds, a 10 pounder would be very skinny with almost no breast. It takes a BB 4-6 months and a hertiage 8-9 months to get to slaughter weight. If you want a smaller turkey then get one of the smaller breeds like a midget white, BSW or something like that. I don't think you will be happy with the carcus from butchering a turkey at such a young age for your 10lb target weight. As for keeping them with chicks, they really should eat a seperate diet of 28-30% protien for the poults and 20% for the chicks. The chicks can eat the higher protien feed but it cost more and chickns are hogs!