Your symptoms are very similar to what mine have been for about 3 years. This all started from being diagnosed with Bell’s palsy in April 2017. I was left with a droopy eye and mouth. My double vision began about 5 months later. That lasted 9 months then seemed to go away. It returned 6 months later. I spent many months with ophthalmologists. Many tests and no diagnosis. Myasthenia Gravis was suspected but blood tests negative. A new Ophthalmologist diagnosed optical M G in th spring of 2019. When I became ill with bronchitis last summer, I was admitted to hospital and was told that 15% of people with normal blood tests for M G have this autoimmune disease. Flares are triggered by illness and your flu could be doing this.
See a neurologist and be checked. I am being treated and am having some relief.
Don’t give up. I pray that you and your husband have big improvements soon.