The problem you are facing is a combination of age and affordability.
While your husband's pension income is acceptable as a form of income for mortgage purposes, his age is causing a problem. This is because most lenders have a cap on how old a borrower must be at the end of the mortgage term.
This is typically 70 or 75 and a shorter term will mean higher monthly repayments. This could explain why you are being rejected as your husband's pension income may not be deemed enough for these higher repayments.
There are a few lenders that can consider cases that run beyond the typical maximum.
For example, Family Building Society judges each case on its merits but can offer loans to borrowers who will be in their 80s by the time it's repaid. Bath Building Society does not have a maximum age so can consider older borrowers where the mortgage will be affordable and Ipswich Building Society could go to 85 years old at the end of the term.