There are two Universal Credit elements for people with limited capability for work:
Limited Capability for Work (LCW) element
Limited Capability for Work and Work-Related Activity (LCWRA) element
You can't get the Carer element as well as one of these limited capability elements. You will get whichever is the higher element. This means that if you are eligible for:
the LCW element and the Carer element - you will get the Carer element only
the LCWRA element and the Carer element - you will get the LCWRA element only
The same applies to each member of a couple except when you are both eligible for the LCWRA element and the Carer element. Only one member of the couple can receive the LCWRA element but the other member will get the Carer element instead.