One of the conditions of receiving carers allowance (CA) is that the person for whom you care is on middle or higher rate of care with disability living allowance, so this should not present any problem.
The point to check out is the overlapping benefit rules you may find that if you get Employment support allowance, the basic rate of which is as you say £67.50 per week, you may not be paid the CA, the basic rate of which is £55.55 per week but you may have an underlying entitlement. So your household income may not be greater after claiming CA, but there may be advantages, which you should investigate with the DWP.