Thanks for sharing this with us, it sounds like a really tough situation that you're in. We see a lot of posts on our forums from parents in blended families and the challenges that parenting in these situations can bring. It must be really hard being told how to parent and having your boundaries disrespected. I understand the kids mum is stopping some contact between you and your partner and the children, I'm wondering what kind of interventions have been made to have a more solid structure around who the children spend time with?
It also must be upsetting that medical decisions and information isn't being shared, I can imagine this must be quite hurtful and concerning. I am going to link some content from the Raising Children's Network about blended families which you might find helpful to have a look at, as well as our own content on some of these challenges.
What you're going through must be incredibly stressful and I'm wondering if it could be helpful to have a chat to someone about this? Parentline is a great service that offers phone counselling to parents from 9am-9pm. Here is a link to their website if you are interested.