What device were they airdropped to exactly? They can only be Airdropped to one device.
Also, do you use iCloud Photos?
On your Mac are they stored in the Photos app or in a folder in Finder?
There are no official Facebook or Instagram apps for Mac, but you can use the website through a web browser to upload the photos.
If they are stored in the Photos app, they would select the Photos location from the Finder window that opens when uploading a photo. You may need to scroll the side bar down to see the Photos location.
If in an older, then just navigate to the folder that holds the photos.
On the iPhone, have you given full access to your Photos to the apps or do you have them restricted to only a few?
If the latter then you can allow Facebook and Instagram access to these photos from their settings in Settings ➜ Apps ➜ Facebook or Instagram ➜ Photos. If you have it set to Limited Access, you can change it to full access or tap on Edit Selected Photos and add the new album so the App can access them.