Sounds like a tremendously hard handover. Poor little guy. He must be emotionally exhausted by the time he goes. It is likely all very anxiety inducing for him, which likely elevates his emotional responses even more so.
Julie, your mothers-mind needs you to tackle this problem with your lovely son. Not LBS-mind. If you can remember that if you get a win for you son, you get a win for Julie. If you get win for julie you may well get one for your H and M.
This is an opportunity Julie, use it as such to bring H closer. We are creating attraction and connection with H and safe handover for you son. These are the goals.
This is an opportunity to do some forward focus thinking and feeling. This is an opportunity to show H, that you can collaborate on resolving an issue together. A highly emotional issue.
Do you think you can put the very fair and reasonable assessments on the back burner.
My initial response is just simply stating a feeling. "Well that felt..........I feel really .......". What do you think?
Let H tell you what he thinks. H is likely to identify a solution. Validate if you think it is something workable....but completely acknowledge the we aspect of finding a solution, " what you said feels doable, I like where you are going, could we build in x and y, they feel like important things to consider for our son. What do you think?
Any time you can use "we" or "us". Throw it in there. If you want to express an opinion, preface it with, my preference would be this, because it would make me feel......What do you think? "
When you are finish that him for sharing his thoughts with you on the matter and appreciate his commitment to his children.
Julie, regarding your lovely boy, sounds like he needs a few things to feel ok about going to dad's. More prep time, there might need to be a transition plan for him, it might have to be incremental. Your sound needs to be support to resolve this and have some control over the process.
Maybe you could talk to him about "what are some things we can think about and do that would make going to dad's easier" .
I know some children need to transition attachment more slowly, so slowing down the process might be key. Dad might need to come in and have a cup of coffee and sit down and then a gradual exiting.
I have never been an advocate of carrying children out of houses in distress, but I am an advocate for supporting children to develop the skills to manage things they don't want to do. Life is about doing things you don't want to do.
If it does get to the point where carrying him out in an upset state is necessary, ask you son what he wants to happen, give him two options or choice. This or that will happen, and let him choose. If he cannot or won't pick one, choose the option for him and let him know in advance. " hey buddy, we know you are upset, but it is time to go with dad, in two minutes, dad or mum are going to pick you up and take you out to the car. If you would like to walk there yourself you can do that too, in fact we would love that"
Julie I know that this is really distressing, and it's not so fair. Working this through is a mum and dad effort. Neither of you should have to wear the bad guy t-shirt, particularly when your sons love each of you.
I have a heap of suggestions for supporting kids with transitions. Someone who would also be good is Grlonfr. She works with her special needs kiddies. She would have heaps of great ideas.