I am sorry to hear of your husband's illness. There is an exemption from meeting the financial requirement that applies where the sponsor in the UK (in this case your husband) is in receipt of one of the following disability benefits:
(i) disability living allowance;
(ii) severe disablement allowance;
(iii) industrial injury disablement benefit;
(iv) attendance allowance;
(v) carer's allowance;
(vi) personal independence payment;
(vii) Armed Forces Independence Payment or Guaranteed Income Payment under
the Armed Forces Compensation Scheme; or
(viii) Constant Attendance Allowance, Mobility Supplement or War Disablement
Pension under the War Pensions Scheme.
If your husband is receiving one or more of these benefits then you will not need to meet the £18,600 income threshold. Under these circumstances it is only necessary to show adequate maintenance and accommodation without recourse to public funds for you, your husband and any other family members who will be living with you in the UK. For example, your family should own or occupy the accommodation exclusively and it should not already be or have the potential to become overcrowded by your joining the household. You will also still have to satisfy the other requirements of this visa e.g. genuine relationship and English language.