I think it's safe to say your husband has not told you anything like half the story. You need to contact his exes, not so your respective kids can all play happy families, but because you need to know why two women who had relationships with him and children with him 'don't let' him see those children. You need to know this so you know whether your own children are safe.
The reason for Ex No 1 certainly will NOT be because her parents have bribed her not to (who the fuck does that? And even if it's true, why on earth would they have taken against him so badly?) or because her current DH is terrified that if the children spend time with their father his wife will be hypnotised by your husband's magic willy and run off with him. Those are such outlandish excuses I am honestly astounded you give them even a moment's credence tbh. Maybe he really DOES have a magic willy if he can persuade you to uncritically accept such a bizarre load of rubbish without proof. As to Ex No 2, 'that mad bitch ex wife" is such a classic again I'd bee surprised if you'd accepted without proof. And as others have said if she had had her child taken from her, as father he should have been the first choice to take responsibility and would have been contacted unless there were very good reasons why not.
All in all he sounds fishy as fuck and I'd be worried.
You say at the start "it's been through the court" then later admit it hasn't (at least in case of DC2). So you are obviously aware the first thing any right thinking person will want to know is WHY your husband hasn't made the effort to be in touch with his kids, and the justified opprobrium that will fall on him for this.
I would be willing to bet one of two scenarios: (a) he's never been near the family court in his life, was a waste of skin as a dad and allowed his children to drift away when his exes did what they could to shut him out of their lives. That's your good option. Option (b) is that he has indeed been to court over access and the outcome went against him. That would be extremely strange, even demonstrably shit and dangerous fathers are usually given some limited access to their children if they fight for it.
The simple way of establishing this (without harassing his exes and their children) would be to ask to see the court documents. If he doesn't have any, or won't let you see them, then you know you are dealing with either a liar or something even more sinister.