Can't send photos by text

Both my father and sister have different phones-  a google pixel and an android.   I have an iPhone 12.   I am unable to send any images to them by text  individually or when they are included in a group text to the rest of my family who all have iPhones.   Can someone help?  I keep getting the red exclamation mark  and "not delivered" message.   I've tried turning MMS and SMS off, resetting network settings, turning them back on...etc. etc.  Still nada.