OP rings a few bells for me and this line in particular stood out: ” He wants to move back to the UK to be closer to family / support but the wife is happy where she is and won’t entertain it.”
I think he is suffering from homesickness and feels trapped due to Work and Family commitments. Having Kids will compound this. In my experience, there is no solution that makes everyone happy.
If he stays, family life will be stable but he will be miserable. If he moves back to the UK, family life will significantly suffer but he will begin to feel better within himself. Being an immigrant is hard and its not for everyone. Its OK to admit that but you then have to deal with the consequences and minimise hurt to all involved.