Put the two smaller ones on the bottom grate. If they're done before the larger ones on the top grate you can pull off the grate through the door by spinning the grate around with a grate tool or something.
Times depend on temp, and since most of us kind of leave the cooker to do it's thing, you'll read all kinds of reports for cook times. Some say as much as 2hr/lb, but if you start with enough lit charcoal and fairly quickly settle in at 250* you can be done in 12 hours. Have a shovel handy for refueling, but I wouldn't dump unlit charcoal briquettes on top of the fire. Either light them in a chimney, or push your coals to the side of the ring and put unlit ones next to lit coals to slowly catch. I prefer to add a combo of lit and unlit.
Hope that helps.
Dave