Carole
Providing he is still able to provide 35 hours of care a week and his doing so is not at odds with his claiming ESA then he should be able to still claim CA.
Carers Allowance is classed as an overlapping benefit with ESA so he can't receive payment of both, depending on the type of ESA he is entitled to either the CA will not be paid and he will receive full ESA or the CA will be paid but deducted from his ESA, they may also be eligible for a Carers Premium.
Get them to put their information into one of the online benefit calculators to get a better idea of what they will be entitled to.
www.gov.uk/benefits-calculators Gordon