If they don't go broody at the same time, in all likelihood the broody will stay on the nest, and the non-broody will visit the nest daily (or as needed) to lay her egg. When the non-broody leaves the nest, the broody will take the new egg and add it to the pile of eggs that she's brooding. As long as there's enough room, turkey hens will huddle into a nest together (and sometimes even when there's not enough room).
The problem with this scenario is that all the different eggs will be on a different schedule, and you'll have a staggered hatch. If they all hatch within 1-2 days, that's usually no problem. If it's staggered over a longer period, then the broody will need to abandon the late eggs to take care of the poults that are already running around, and those partially developed embryos still in the nest will die. Additionally, if the total number of eggs becomes too many for the broody to effectively cover, then your hatch rate drops even further, sometimes very low. If there are too many eggs to cover effectively, then the eggs on the periphery get cold. If they're too cold for too long, the embryos die. Because the hen will turn and rotate the eggs, every egg that takes a turn on the periphery can potentially die. Only the eggs that stay in the center will develop to term and be able to hatch, which may be all the original clutch, or half, or none. Too many eggs under a broody is not a good thing.
What most people do is collect eggs that they want to hatch. Write the date they were laid on them. Do not wash them or get them wet at all, even if they are visibly soiled, but you can lightly brush them off with a clean towel or paper towel. Store them pointy end down in a carton in a room that is 50-60 degrees, warm enough to keep the embryo alive but not so warm that it will start developing yet. Tilt them about 45 degrees, and alternate the direction of tilt 3-4 times daily. They can be stored this way up to 10-14 days, but hatch rates start to decrease around day 7. When a hen goes broody, put some labelled throw-away eggs or ceramic eggs under her for 2 days to be sure that she is committed to brooding. Once you're sure that she's really going to brood, and she's in a safe place, you're ready to put the real eggs under her. Draw a circle around the outside of each egg so that you can identify that egg no matter what position it's laying in. Exchange all the throw-away eggs/ceramic eggs for all the saved eggs all at the same time, at night, with as little disturbance and drama as possible. That way the incubation of all the eggs will start at the same time, so you should have all your poults hatch quite close together. If there's another hen that will lay eggs in the broody nest, check the nest every 1-2 days and remove all new eggs to prevent a staggered hatch, and to prevent an excessive number of eggs under the broody. If you have eggs stored more than 7 days (or 10-14 at the most) without a hen going broody, then you can rotate the 8-15 day old eggs back into the refrigerator to eat. As long as you don't wash the bloom off the eggs (the oxygen permeable "sealant" that prevents bacteria from penetrating the shell), eggs can safely last for quite a long time out of the refrigerator.
Messes up my WHOLE system!
