>>Is the minimum the gov.UK website for child support and half the mortgage?
No, this is a common misunderstanding. So far as children are concerned what is payable in most cases is according to a formula on the government website. However, there is NO obligation to pay half the mortgage or half of anything else. Your wife has the benefit of living at the property and you do not so there is no obvious reason why you should subsidise her accommodation costs. That is not to say that you might not be liable to pay something but that is assessed on needs and resources rather than upon any automatic paying of half of anything.
Say, for instance, you earned £100K a year and your wife had always been a stay at home mum with no independent income of her own. In that event you would almost certainly need to pay her some spousal maintenance so that she could meet her outgoings including the mortgage. Say, on the other hand, that you each earned £50K a year. Under those circumstances she could almost certainly meet her own outgoings and she would be unlikely to have any claim upon you.
The details of your respective needs and resources are what matter here rather than any notional obligation to pay half of anything.
>>Can she demand I pay half of everything or more?
See above.
