Messaging is kind of a mess on Android. Right now your phone uses MMS to send photos/videos to iPhone users which compresses them. Google is trying to get carriers to implement a universal profile for RCS which will basically replace SMS/MMS to provide an iMessage like experience, it will also fall back to SMS/MMS as needed. Apple will also have to build this into their Messages app and I haven't read any information if Apple will support this or not.
Some workarounds:
You could upload the photos to Google Photos and send links in text messages to the full resolution photos/videos.
Could have people install an IM app such as: Signal, WhatsApp, Telegram, Facebook Messenger.