Assign a stable group with 0 or 1 nether in it. This stable group should have the exact creatures you plan to nether for the final team.
Now, take out the nether from your current party.
Use a potion of transforming on a creature of your choosing.
Repeat steps 2-3 for however many nethers you need.
Reload your saved stable group
Multple nethers are now present in your party.