Group chat problems from note 5 to iphone?

I'm trying to text in a group chat with people but it says that they're messages are trying to send as imessage and they have to go back into settings and turn it off every time they want to talk to me but they don't feel like doing it every time so we use groupme bUT it kinda sucks. Is it it my problem or theirs?

I messaging is only for iPhones so

You can only send it through iPhones and you could try LEO Privacy Guard 3.0 in order to gain total Security for your device.