First, I’m sorry your husband and your family are dealing with the Parkinson’s and LBD. As someone who’s kept a family member with a progressive/degenerative disease at home instead of moving her to a facility I appreciate the stresses involved and you have my sincerest well wishes. Even with outside help, it’s daunting. Now, regarding your options for a replacement stove top: Is that a portable two-element cooktop I see to the right of the cooktop? If not, you might want to buy a portable induction cooktop just to take the pressure off while you investigate a more permanent solution. If you give me the model number of your current cooktop and downdraft, along with some pictures of the blower unit underneath, I’d be happy to help. (I too have a Thermador with telescoping downdraft in my island, circa 2000, but it’s in the form of a 30” dual-fuel drop-in range.) If you could also wrap a flexible measuring tape (or even a piece if string and then measure that if that’s all you have) around the ductwork that the blower is connected to, that’d be very helpful. I’d hate for you to find a replacement that requires larger diameter ducting that can’t easily be installed. Btw, are you on a crawl space, basement or slab?

P.S. What’s above the island, attic space or living space? Would you consider overhead ventilation if it was feasible to install it over the island?

P.P.S. If you’re best option requires a smaller countertop cutout, are you willing to replace the island top? Unfortunately, with laminate, you can’t really reduce the size of an opening. At least not in an inconspicuous/aesthetically pleasing way.