iMessages sent from icloud address/phone number=2 conversations!

This is a long-standing issue that defies resolution. At times, my iphone or my wife's iphone will send iMessages from our iCloud addresses instead of our phone number. So if my wife sends an iMessage to me, I sometimes get a new message from "julie.surname@icloud.com". Although her name, email addresses and phone number are in my Contacts, this new conversation shows up as her email address. We used to think it was because she travels abroad and uses wi-fi in her hotel that caused the phone to use an email address rather than her number because she was out of the UK. Not so! Here's what happened today: My wife sent me and our 2 children iMessages from London Heathrow to us three at home. My message came through as from her email address, my daughter's also came through from her email address, but my son, a few yards down the hallway got his from her phone number.

This is a typical scenario which can work the other way round when it's ME sending her the iMessages where she gets my message as though I'd sent it from my email address rather than the phone number.

I have been through all the hoops I know of to sort this but I just can't fix it. I don't know whether it's the iPhone, iCloud or what that's at fault. But it is driving me mad.

In this morning's case, I replied to her message by using an older (yesterday's) conversation to send my iMessage to her, and her reply to that came to me via her phone number, as expected, and good as gold. Had I just replied to her iMessage, it would have perpetuated the TWO conversations. I have tried logging out and back in, deleting the accounts and reinstating them, re-entering the settings, making sure that the "Start new conversations from..." is set up correctly and so on. Then after a while, it returns, randomly, to sending texts from the email and starts a new conversation again. And you can't combine the 2 conversations even when you go to Details-Add to existing contact etc.

I have also just been informed by a supplier that my iMessages to him are showing up as my email address not my phone number, despite my iphone being set to 'Start conversations from +44777...etc"

Please throw out suggestions as you wish and I'll be grateful, even if it's one I've already tried and failed with.

This icloud is a nightmare.

Many thanks in advance.

Chris

iphone 6, latest iOS