Hi @unclemontyscrumpets. It seems you've run into the crowd who believe that fathers are second class citizens. I'm afraid that you'll find a lot of them on here. However, they are wrong - both ethically, and in law.
I totally get where your husband is coming from - there are plenty of mothers who make a point of trying to exclude fathers from major decisions about the child(ren). It's just a form of controlling behaviour.
The legal position is that, as your husband has PR, he is an equal parent and should be involved in major decisions about his child. Not the day to day stuff - when the kids are with him, he gets to make those calls; and when they're with their Mum, she gets to. But the big stuff - major medical decisions, school choices, and other important matters absolutely should be discussed between the child and both parents. That shouldn't be about either parent trying to impose their view on the other - it should be about constructive co-parenting, in the best interests of the child. It sounds as though that's what your husband is after, and that's both reasonable, and the sign of a responsible, involved parent.
Given that his ex is actively obstructing a constructive co-parenting relationship, he may wish to consider mediation on that specific subject, to see if they can agree some ways of working together, that they can both commit to. Of course, she may not agree to that - again, it might just be about power for her.
If that's the case, his best mechanism for involvement actually comes through his relationship with his kids. He sees them for at least a couple of days a week, so it's important that he maintains a close relationship with them and stays sighted on what's happening in their lives. That gives him the best chance of being aware of things that are coming up, where he may wish to guide the child, or become more actively involved in major decisions.
He should also familiarise himself with timelines for things like school applications, so that he can proactively engage with the child and his ex to discuss those issues in good time.
Finally, he should stay in contact with schools etc, and ensure they know the child's circumstances. Schools have a legal obligation to share information with all parents of a child. And he should ensure he attends parents evenings etc - it should be second nature for him to be involved with his child's life. It may not stop his ex being obstructive - my ex and I have 50/50 with our daughters, so there is no RP or NRP. But that doesn't stop her actively telling schools etc that they should be talking to her and not me (despite her often not bothering to attend parents evenings etc). Again, control. But a constructive relationship with schools and others can usually overcome those issues - they usually see pretty quickly when one parent is trying to be controlling.