A lot of people say that ANA IC has the best location ... I usually wonder, for what? Certainly good if your business is nearby, but for tourists, the immediate neighborhood is really drab IMO, not a pleasant walk to Roppongi (which is the pits anyway), and it's not super convenient for getting around by Metro. It's quite central if one travels by taxi (which is of course cheap these days due to the exchange rate), and the #1 bus runs from Shibuya to Shimbashi. So perhaps you're right, not bad for aging parents?

Certainly, if hikouki's dad can walk but needs to sit down after a few blocks, Tokyo will be challenging. For instance, the walk from IC Strings to the Yamanote line tracks is not unlike the walk he might experience at an airport, from check-in to gate, in terms of distance and crowds. I'd pick whatever hotel offers the best deal, knowing that none of them are superstar ICs (try IC Osaka for that), and make plans that involve short taxi trips and opportunities for the elderly travelers to rest -- as benches are rare, you may have to sit down at a business and consume something (at the low end, and available anytime, many convenience stores have corners where you can sit and sip a cup of coffee). Also worth keeping in mind for elderly parents are "multipurpose" bathrooms (denoted by the wheelchair symbol), which often have a fold-out that would allow a weary traveler to lay down for a few minutes (found e.g., in department stores).