Super confused with what you are asking but I will chime in with my experience from moving froim iOS to Android.Issue:
My friends who are using an iOS device AND using iMessage cannot text me.Reason:
Before I moved away from iOS to Android I should have disabled iMessage on my device.
before moving platform.
Sure my friends who are still on iOS devices and using imessage can text me BUT they have to wait for the text to fail and then 'press & hold' the failed text and select 'send as SMS'
I also called Apple and explained to them the issue and they had no record of my device ever using iMessage
so they had me delete the 2 iphones that were tied to my support account AND reset my appleID password.
Didn't do a damn thing.
I'm guessing that from your story above that one of the iphones did not have imessage enabled before the change = hence they are able to have replies sent to them.