Need a bit more specifics. ECDH handles this already like we do in nip04 and nip44. This would require encrypting the plaintext for each person then passing it. There is really no way to avoid that. You will have to share some piece of information individually with each user. If you opt for the nip04/nip44 mechanisms then the user's already have the required information needed for encryption/decryption. 

There would be no "universal decryption" mechanism where you can have the same ciphertext encrypted in such a way that a select group of users would be able to decrypt.  

 That's what I thought. Thanks.