I hate to admit this, but I work in child support enforcement.
But I'm in the US, here emancipation occurs at age 18 and doesn't usually extend for university.
My State's guidelines calculate both parents income, including certain expenses, such as the non-custodial parent having a second family.
For basic purposes, let's say it costs $300 (or pounds) a month to care for a child. One parent makes 1200 a month and the other makes 800, which is 2000. The parent that makes 800 a month is responsible for 40% of the child's care and the other parent is responsible for 60%. If the absent (non-custodial) parent makes the 1200 a month that person is responsible for 60% of the $300 to raise the kid.
See if you can find a child support calculator for your area.
As far the 19 year old goes, if it's not mandatory to provide support, do what you can to help him along into adulthood.