I would start out with straw for bedding, keets are notorious for eating shavings and getting impacted (and dying from it).
They may not need heat during the day since it's summer, but I'd provide a lamp that gives them an area under it with a temp of about 75-80 degrees. Make sure they can get out of the heat if they need to.
Also keets (Guineas in general, any age) can get freaked out by changes, so you may want to start off with containing them to a small area of the coop for a while at first... otherwise they may huddle in a corner and get chilled, or not be able to find their feed and water.