Hi Grandma1967
Your child will no longer be a Qualifying Young Person when he starts the course leading to a university degree level qualification. So as you say you will lose the UC child element. He will then be classed as a non-dependant. As such his income will not affect your UC. You may be exempt from the UC Housing Cost contribution on the disability criteria.
Once 18 he becomes an adult for Council Tax purposes and if you are in a Council Tax Reduction scheme then it will need to be recalculated.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
