The four headrest pieces are glued up in 2 steps. Because of the angled sides it is hard to glue them up all at the same time. I will glue pcs 1 and 2 together. I will then glue pcs 3 and 4 together. Let them set overnight. The next step involves gluing the 2 halves together. Again because of the bevels you will need to add some clamping scraps to the sides to be joined for your clamps to grab hold of. Take care to place these scraps square to the headrest joint. If they are off, the clamping will be misaligned. The scrape pcs should overhang the headrest by 2 inches or more to allow the clamps to grab in the next step. My headrest pcs are 7 to 7 1/2" high so the scrap pcs will be 11 - 12" long. Before gluing the strips to the headrest, bevel the edge that the clamps will be tighten up against. The bevel should be 9 degrees again. If you don't bevel this edge your clamps will tend to slid off and you will have to add beveled shims to keep them online. I sometimes forget so I still look at my picture log book to remind me. This reminds me of a tip. Get a nice digital camera and take lots of pics. Lots of pics. You can always delete the ones you don't want. You will find yourself looking at them on your next chair build over and over. These scrap pcs will be cut flush with the headrest pcs after glue up and then final cut from the body prior to the bandsawing of the curve. I rough cut them off using my bandsaw. 
In the picture you will see the grooves for the biscuits. I double biscuit to help in the alignment. Again, because of the bevels, the more you do to prep your pcs the easier it will be when gluing and the headrest will sit level and plum on your workbench. This helps later during the bandsaw process. Let the pcs sit overnight for a good solid hold. The strips will be asked to hold the next glue up step.
In the picture you will see the grooves for the biscuits. I double biscuit to help in the alignment. Again, because of the bevels, the more you do to prep your pcs the easier it will be when gluing and the headrest will sit level and plum on your workbench. This helps later during the bandsaw process. Let the pcs sit overnight for a good solid hold. The strips will be asked to hold the next glue up step.The next and final glue up is ready. You can make a jig to hold the pcs. I use my great grandfathers workbench and vise to hold the parts. The wood clamps are also my great grandfathers. I like them because they can adjust to slight angles and I can really get a good grip on them and tighten until I see the glue squeeze out. Add the bicuits, spread the glue and clamp the 2 half sections together and let set overnight. Take care to line the joint up as it will make the following steps easier. 
Patience is hard when you have to wait til the glue dries or you want to get going on the next step. I find myself constantly wanting to jump ahead but learned over the years not to. Keep telling yourself how much you spent on the material. This should help you take your time. These chair parts are all so interwound on each other that making a mistake may cause you to start over. It's not the worst as sometimes that is the best learning tool but it's expensive. Don't get scared into not wanting to try but think ahead as in the game of checkers or chess. Measure and prefit, measure and prefit and then measure and prefit again. After the joint has set you are ready to cut the curve. I use the bandsaw for a rough curve and then my router in a jig I made to final finish the shape. After that, it's a whole lot of hand work and sanding. Some of the final sanding I do before I attach the headrest to the back leg assembly. You can just leave it as is after you use the router until it's attached. Once you attach the headrest more shaping and sanding will need to be done so it's okay if it's a little rough at this stage. Most likely after attaching to the legs you will need to change the profile a little. Now on to rough shaping the headrest as a whole finally glued up piece.
Patience is hard when you have to wait til the glue dries or you want to get going on the next step. I find myself constantly wanting to jump ahead but learned over the years not to. Keep telling yourself how much you spent on the material. This should help you take your time. These chair parts are all so interwound on each other that making a mistake may cause you to start over. It's not the worst as sometimes that is the best learning tool but it's expensive. Don't get scared into not wanting to try but think ahead as in the game of checkers or chess. Measure and prefit, measure and prefit and then measure and prefit again. After the joint has set you are ready to cut the curve. I use the bandsaw for a rough curve and then my router in a jig I made to final finish the shape. After that, it's a whole lot of hand work and sanding. Some of the final sanding I do before I attach the headrest to the back leg assembly. You can just leave it as is after you use the router until it's attached. Once you attach the headrest more shaping and sanding will need to be done so it's okay if it's a little rough at this stage. Most likely after attaching to the legs you will need to change the profile a little. Now on to rough shaping the headrest as a whole finally glued up piece.