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Proving there is nothing else preventing your husband from being eligible for Income Related ESA such as your savings, see
Asset and savings rule for ESA(IR) or other income such as a pension then he should be able to add you to his claim.
What awards of PIP do you both have? If you both have Daily Living awards and no one else lives with you then you should also be eligible for the couples rate of the Severe Disability Premium, about £120/week.
Put your information into one of the online benefit calculators to get a better idea of what you might receive.
www.gov.uk/benefits-calculators Gordon