With poultry- whole bird- the Rivet-Rule-O'-Thumb is 50% is bone and thus not edible.
For 27 people at 1/3 to 1/2 LB per person you are looking at 14 LBS of meat, near 30 LBS of whole turkeys.
Recommend three 10 to 12 pounders over two 15 pounders cause your cooking times will be less. Less meat-mass, less cooking time.
You've got yourself a challenge, buddy, hang in there
cause you can make it happen really well! Keep us posted and know there is someone here who can give you advice as you cook....just post, you'll get results.
Good luck to you and congratulations on the vote of confidence from your eaters!