But the real, much bigger problem is that you are engaged to marry a man who doesn’t support you, criticises your parenting and thinks your 4 year old is somehow grabby. These are not the sort of views that a good father, stepfather or husband would hold. He is not a catch.
It's clever how they've got you thinking what a great match this is by telling you you've transformed him, and how wonderful you are compared to the evil ex. It's an extremely manipulative and worrying approach to take with a new partner, that you usually only see when people are trying to stop somebody from listening to their instincts about the little niggly "off" things going on around them.
I take no issue with blended families, but I do find it troubling that you seem to have been swept off your feet and are being rushed headlong into a marriage without time to step back and evaluate things clearly - especially with everything else going on. It comes across like they're trying to get you tied down before you have a moment to really know them or make any alternative choices.
If you didn't have people spinning you this beautiful web of the fabulous future you'll all have together, and pressuring you to have this rushed, extravagant wedding, do you think you'd react differently to the idea of legally joining yourself to a family who have repeatedly mistreated your children, blamed the young children for the distress they experienced as a result, and completely disregarded and disrespected you on it all?
You're their mother, and instead of taking on board your concerns you were told that you were wrong and it was actually the failing of a four year old child. That's so disrespectful. Somebody who loves you would listen and respect you.
In any other circumstance, would that make you want to slow things down? Slowing down doesn't mean giving up, or not being committed if that's your concern in saying you'd like that to happen.
If you're the perfect match everyone is saying, then there's no need to hurry, is there? You'll be together regardless, with time to establish boundaries and respect. Time to ensure your children aren't knowingly hurt and then blamed. Time to make sure there's nothing to make you need to come and ask us if you're being oversensitive or if there is something truly wrong.
What would happen if you asked for the wedding to be brought back under your own control, and to take place at a future date once all these issues are comfortably ironed out, and you don't have so much to deal with in your life?
It's your life, you're allowed to be the one in control of it.