Hey there, Goofy6067!
Thanks so much for using Apple Support Communities.
We want you to be able to message all of your contacts, certainly not just the ones who use iPhone. To do that, we want to first make sure that you're not experiencing any issues with making calls and sending messages more broadly. It sounds like you may have worked on isolating the issue to Android-using contacts, but just to be safe we want to share these resources:
If you can't make or receive calls on your iPhone
If you can't send or receive messages on your iPhone, iPad, or iPod touch
If you're still experiencing the issue after that, we're wondering if the ones who you can't message recently changed over to Android from iPhone? If that's the case, then they may need to deregister iMessage by following these steps: Deregister iMessage. Just as a note, those steps will need to be performed by the contact you're messaging and not by you, yourself.
We hope that this information is helpful.
Have a great day!