Getting 50/50 childcare

Hi,
I’ve been separated for nearly 3 years and divorce going through. We sold family home and both have new homes.I have been having my 2 children when I’ve not been working. As a shift worker this is not set in stone but have had them on average between 10 and 13 nights a month. My ex works abroad 10 days a month in a 14 day period then 14 days off, and family have been helping when we are both at work. I provide her with the dates I can have my children in advance. I then get the given the dates that she dictates that I can have them. I asked if could do a week on/week off but this wasn’t acceptable for her. Have now asked her for me to have them for the 14 day period she is contracted to work. My family can help with childcare if I am at work. This also hasn’t gone down well. The last few months my childcare has reduced to 8 nights a month for no reason despite being able to have them 14. I’m fed up with not getting enough time with them and they always say they want more time with me. Where now do go, I suggested mediation but she thinks it’ll be a waste of money and time. How do I apply to court to get more time with them and what are my chances? I think it is not unreasonable to get 2 weeks on / 2 weeks off with me even suggesting that if she had a few days off in that period then we could swap with me having them the same amount of time on her time it’s them.

Hope this makes sense?
Thanks
Gas