Dave sounds extremely controlling.
He doesn't want to see the kids to rebuild a relationship with them; he wants to see them to win. Otherwise - even before factoring in the 2 years of flakiness and 3 years of complete absence - his first concern would be meeting their needs and avoiding harm. He'd be jumping at the chance of seeing his daughter, rather than using her as a tool for leverage. That's sick.
I dont reckon either of them behaved without reproach in the whole thing
I find it a little weird how you keep going out of your way to give examples of how Emma failed to be perfect in all of this. Can you name a perfect human for us?
Just because she may not have been perfect, doesn't mitigate or excuse his shitty behaviour.
she felt very powerless in their relationship and I think being in control sometimes was more important than trying to work together
You know this is not a description of a normal situation, right?
If this is the kind of controlling, manipulative behaviour he's happy to share with the world, how bad do you think he was behind closed doors for Emma to have felt so powerless she clutched at any means she could to bring some semblance of control back into her life.
Which, by the way, is an extremely common response from women suffering coercive control at the hands of their partner. As humans we need to feel we have some control over our lives, and when this is taken away we do desperately claw at anything else.
People who like taking control away from other people are abusers (whether you think they look like a monster or not).
Asking for initial contact by letters after abandoning them in the past seems a sensible safeguard to ensure he isn't just using them as a control tactic (which he seems to be given his reactions) and that he won't get their hopes up only to let them down and hurt them again. He has trust he needs to earn and commitment to demonstrate, and being a controlling arsehole isn't going to achieve that.
You've even said you'd expect courts to suggest the same, yet then try to make out Emma is being unreasonable for wanting this step first. Why? Emma doesn't seem to be able to do anything right in your eyes.
He doesn't sound stupid, he sounds abusive.
Before you leap to his defence that you've never seen him be abusive - what you describe here is a form of abuse, and unless you are actually Emma or Dave then you have no idea how he behaved behind closed doors, but the way he made Emma feel strongly points to him having been even worse.
Why is it you think Emma is being an idiot for wanting to protect these children from being hurt again? Children don't just shrug off being abandoned by a parent. It has a lasting impact.
She seems to be acting in their best interests - what would you have her do, force the son to see his father against his will and put them both at risk of being abandoned again with no safeguards and no attempt to heal the lasting damage caused by Dave?
I have no trouble seeing why you'd call him an idiot for trying to use children as a way to exert control over Emma and to make himself feel powerful.
There doesn't seem to be anything Emma could do that you would consider acceptable, other than capitulating to his demands and enforcing contact on an unwilling child. Are you Dave?